This is a phase III clinical trial to evaluate the efficacy and safety of SHR6390 in combination with Fulvestrant versus placebo combined with Fulvesrant in Patients who have HR positive and HER2 negative recurrent/metastatic breast cancer and have received prior endocrine therapy are eligible for study.

Inclusion Criteria:

1. Has the pathologically-confirmed diagnosis of locally recurrent or metastatic, hormone-receptor positive, HER2 negative Breast Cancer.
2. Age: 18 - 75 years old, postmenopausal women or prepostmenopausal women
3. Received prior endocrine therapy
4. One previous line of chemotherapy for advanced/metastatic disease is allowed in addition to endocrine therapy.
5. Eastern Cooperative Oncology Group [ECOG] 0-1

Exclusion Criteria:

1. Patients who received prior treatment with any CDK4/6 inhibitor, everolimus or fulvestant.
2. Clinically significant cardiovascular and cerebrovascular diseases,including but not limited to severe acute myocardial infarction within 6 months before enrollment, unstable or severe angina, Congestive heart failure (New York heart association (NYHA) class > 2), or ventricular arrhythmia which need medical intervention.