This open label, single-arm, Phase 2 study aims to evaluate the efficacy and safety of Anti-FcRL5 CAR-T in subjects with relapsed and refractory multiple myeloma. A leukapheresis procedure will be performed to manufacture. Anti-FcRL5 chimeric antigen receptor (CAR) modified T cells. Prior to Anti-FcRL5 infusion subjects will receive lymphodepleting therapy with fludarabine and cyclophosphamide. After infusion, the investigators will observe the characteristics of dose limited toxicity (DLT), and determine the maximum tolerable agent MTD and rp2d were confirmed. To provide basis for the dosage and treatment plan of cell products in follow-up clinical trials.