Capecitabine combined with pyrotinib is the standard protocol for HR+/HER2+ advanced breast cancer after trastuzumab failure, but the incidence of grade 3 hand-foot-syndrome was 16.4%. Therefore, the search for efficient and low toxicity alternatives has become a research hotspot. Our previous basic studies have shown that ER inhibitor fulvestrant and HER2 inhibitor pyrotinib have a synergistic effect. The preliminary analysis of our prospective shows that the efficacy is close to that of capecitabine combined with pyrotinib, and the adverse events are significantly improved compared with capecitabine combined with pyrotinib. Therefore, it is necessary to further carry out a head-to-head phase III randomized controlled clinical trial to study the efficacy and safety of fulvestrant combined with pyrotinib in the treatment of HR + / HER2 + advanced breast cancer.