This is a multicenter, randomized, single-arm, open-label Phase II study to evaluate the efficacy and safety of Mitoxantrone Hydrochloride Liposome Injection with different doses in participants with Relapsing Multiple Sclerosis. Participants will be randomly enrolled into three treatment groups: Mitoxantrone Hydrochloride Liposome Injection 4 mg/m^2 group, Mitoxantrone Hydrochloride Liposome Injection 8 mg/m^2 group, and Mitoxantrone Hydrochloride Liposome Injection 12 mg/m^2 group. The primary outcome measure is the cumulative number of new Gd-enhancing lesions at the end of 48 weeks of Mitoxantrone Hydrochloride Liposome Injection treatment in brain MRI.