Inclusion Criteria:

          1. Subjects voluntarily joined the study, signed informed consent, and had good
             compliance.

          2. Female patients aged 18-75 years (including cutoff value).

          3. Patients with HR+/HER2+ recurrent or metastatic breast cancer confirmed by
             histopathology

               -  HER2 positivity is defined by standard of 3+ staining by immunohistochemical
                  staining (IHC) or positive for in situ hybridization (ISH)

               -  Estrogen receptor(ER) or Progesterone receptor(PR) positive is defined as the
                  percentage of cells positive for ER or PR expression ≥ 1%

               -  Local recurrence needs to be confirmed by the physician that is unresectable

          4. At least one extracranial measurable lesion according to Response Evaluation Criteria
             in Solid Tumors (RECIST) criteria version 1.1.

          5. Natural postmenopausal women, or women who have undergone bilateral oophorectomy.

          6. Prior treatment:

               -  Previously received no more than 1 prior lines of systemic treatment with
                  trastuzumab regimen for repetitive metastatic diabetes [including anti-HER2 ADC,
                  subsequent meaning is the same]

                    1. The early stage includes trastuzumab-containing regimen treatment， or
                       trastuzumab-containing regimen that relapses more than 1 year after the end
                       of adjuvant treatment, and subsequent treatment is included as the
                       first-line anti-HER2 treatment;

                    2. The first-line treatment fails with the trastuzumab-containing regimen, or
                       the trastuzumab-containing regimen recurs during the adjuvant treatment or
                       relapses within 1 year after the adjuvant treatment ends, the follow-up
                       treatment will be included as the second-line anti-HER2 treatment;

               -  Have not received anti-HER2 TKI treatment before or received but did not prove
                  that the treatment failed;

               -  Past endocrine therapy has not proven resistance to aromatase inhibitor therapy
                  (resistance defined as: recurrence during or within 1 year after the completion
                  of adjuvant aromatase inhibitor therapy, received aromatase inhibitors and
                  disease progression in the recovery stage of metastasis).

          7. Eastern Cooperative Oncology Group Performance Status of 0-2.

          8. Life expectancy ≥ 12 weeks.

          9. Adequate function of major organs meets the following requirements (no blood
             components and cell growth factors have been used within 14 days before
             randomization):

               -  Neutrophils ≥ 1.5×10^9/L

               -  Platelets ≥ 90×10^9/L

               -  Hemoglobin ≥ 90g/L

               -  Total bilirubin≤ 1.5 × the upper limit of normal (ULN)

               -  ALT and AST ≤ 2.5 × ULN

               -  BUN and Cr ≤ 1.5 × ULN

               -  Left ventricular ejection fraction (LVEF) ≥ 50%

               -  QTcF(Fridericia correction) ≤ 470 ms

               -  International normalized ratio(INR)≤1.5 × ULN，activated partial thromboplastin
                  time(APTT) ≤ 1.5 × ULN

        Exclusion Criteria:

          1. The subject has untreated central nervous system (CNS) metastases.

          2. Patients who have undergone systemic, radical brain or meningeal metastasis
             (radiotherapy or surgery), but have been confirmed to have been stable for at least 4
             weeks, and who have stopped systemic hormonal therapy for more than 2 weeks without
             clinical symptoms can be included.

          3. Previously received any CDK4/6 inhibitor treatment.

          4. There are ascites, pleural effusion, pericardial effusion with clinical symptoms at
             baseline, those who need drainage, or those who have undergone drainage of serous
             effusion within 4 weeks before the first dose.

          5. Inability to swallow, intestinal obstruction or other factors affecting the
             administration and absorption of the drug.

          6. Received systemic therapy such as chemotherapy, molecular targeted therapy or other
             clinical trial drugs within 4 weeks before enrollment; received endocrine therapy
             within 2 weeks before enrollment.

          7. Patients with other malignant tumors within 5 years or at the same time( except for
             cured skin basal cell carcinoma and cervical carcinoma in situ).

          8. Have undergone major surgical procedures or significant trauma within 4 weeks prior to
             randomization, or are expected to undergo major surgery.

          9. Pregnant women, lactating female, or women of childbearing age who are unwilling to
             take effective contraceptive measures.

         10. Have a history of allergies to the drug components of this regimen.

         11. Patients with active HBV and HCV infection; stable hepatitis B after drug treatment
             (HBV virus copy number is higher than the upper limit of reference value) and cured
             hepatitis C patients (HCV virus copy number exceeds the lower limit of detection
             method).

         12. History of immunodeficiency, including HIV positive, or other acquired or congenital
             immunodeficiency disease, history of organ transplantation.

         13. History of cardiac dysfunction, include(1)angina (2)clinical significant arrythmia or
             require drug intervention (3)myocardial infarction (4)heart failure (5) other cardiac
             dysfunction (judged by the physician); any cardiac or nephric abnormal ≥ grade 2 found
             in screening.

         14. Female patients who are pregnancy, lactation or women who are of childbearing
             potential tested positive in baseline pregnancy test.

         15. Childbearing female who refuse to accept any contraception practice.

         16. Determined by the physician, any serious coexisting disease might be harmful to the
             patient's safety or avoid the patients from accomplishing the treatment(e.g serious
             hypertension, diabetes, thyroid dysfunction,active infection etc.).

         17. History of neurological or psychiatric disorders, including epilepsy or dementia.

         18. Severe infections within 4 weeks prior to first dose (eg, intravenous infusion of
             antibiotics, antifungal or antiviral drugs according to clinical protocols), or
             unexplained fever (T > 38.3 °C ) during screening or prior to first administration.