The clinical trial was designed as a single-arm, open-label clinical study, with the main purpose of exploring the safety, pharmacokinetics, and best recommended dose (RP2D) of the UTAA17 injection in the treatment of relapsed or refractory multiple myeloma (r/r MM) subjects, and also the efficacy will be observed. Eligible subjects will accept the infusion of UTAA17 injection after pretreatment, and their blood will be collected before and after infusion for evaluation of pharmacokinetics, immunogenicity and safety. This study plans to evaluate efficacy using the revised Evaluation of Efficacy in multiple myeloma -IMWG criteria (2016), which will be evaluated at 4w, 2m, 3m, 6m, and 6 to 24m (at a frequency of Q3m) after cell reinfusion, in addition to the baseline period. Efficacy evaluation continues until one of the following occurs: subject disease progression (PD), acceptance of a new antitumor therapy, death, occurrence of intolerable toxicity, investigator decision, or patient decision to withdraw.