• 1.Aged 18-75 years (inclusive of 18 and 75 years old), gender not limited;

• 2.Subject has received at least 3 lines of therapy, including at least proteasome inhibitors (PIs) and immunomodulatory therapy (IMiD); disease relapse, progression, or refractory according to the International Myeloma Working Group (IMWG) Consensus (2016) criteria for multiple myeloma;

• 3.Subjects whose tumor specimens were positive for BCMA expression on the membrane surface of plasma cells by immunohistochemistry (IHC) or flow cytometry and had not received prior BCMA CAR-T therapy;

• 4.One of the following is met (all data below are compared to the obtained minimum values):

• \- a. Serum M-protein increased by more than 25% (absolute increase greater than 5 g/L) or M-protein increased by more than 10 g/L (if baseline serum M-protein is greater than 50 g/L);

• \- b. Uroprotein increased by more than 25% (absolute increase greater than 200 mg/24h);

• \- c. The difference between affected and unaffected serum FLC increased by more than 25% and the absolute value increased by more than 100 mg/L;

• \- d.The proportion of bone marrow plasma cells increased by more than 25% and the absolute value increased by more than 10%;

• \- e. The sum of the original maximum vertical diameter products of more than one measurable lesion increased by at least 50% from the lowest point; or the long axis of the original lesion of at least 1 cm increased by at least 50%;

• \- f. An increase in circulating plasma cells of at least 50% (used when only circulating plasma cells are measurable lesions, with an absolute value of at least 200 cells per microlitre);

• 5.ECOG performance status score of 0-2；

• 6.Expected survival ≥12 weeks；

• 7.Subjects must have adequate organ function and meet all of the following laboratory test results prior to enrollment:

• \- a.Complete blood count: Neutrophil count (ANC) 1E9/L; Lymphocyte count (ALC) 0.5E9/L; Platelet count \>50E9/L; Haemoglobin \>60g/L or Haematocrit \>0.24；

• \- b.Liver function: Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) less than 2.5 times the upper limit of normal (ULN); serum total bilirubin less than 1.5 times the ULN;

• \- c.Renal function: The creatinine clearance rate calculated according to the Cockcroft-Gault formula is GFR 40ml/min (except for those whose renal function is abnormal due to progression of the primary disease as judged by the investigator);

• \- d.Coagulation function: fibrinogen ≥ 1.0 g/L; activated partial thromboplastin time ≤1.5×ULN, prothrombin time (PT) ≤ 1.5×ULN;

• \- e.Blood oxygen saturation \> 91%;

• \- f.Left ventricular ejection fraction (LVEF) ≥ 50%;

• 8.Subjects and their spouses agreed to use effective instrumental or medical contraception (except for safe contraception) from the time of signing the informed consent form until one year after CAR-T cell reinfusion;

• 9.Participants must personally sign a written informed consent form approved by the Ethics Committee prior to the start of any screening procedure.