This is a single-arm, phase Ib/II study to investigate the safety and efficacy of mitoxantrone hydrochloride liposome combined with enlonstobart in the treatment of relapsed and refractory peripheral T-cell lymphoma, and the optimal dose of mitoxantrone hydrochloride liposome. In the dose-escalation phase, the initial dose of mitoxantrone hydrochloride liposome injection was 16mg/m2, and two dose groups of 16mg/m2, 20 mg/m2, D1, q4w were designed. Enlonstobart was administered at a fixed dose of 360mg, D1, q4w. Dose-limiting toxicity (DLT) was assessed after cycle 1. Six cycles of induction therapy were planned. After induction therapy, if the response evaluation was CR/PR, maintenance treatment with enlonstobart (360mg, D1, q3w) could be performed.