Melasma is a common and refractory pigmentary skin disorder manifested as light to dark brown patches on the facial skin. It belongs to disfiguring dermatoses and significantly affects the physical and mental well-being of patients. Conventional treatments for melasma, including pharmacological and photoelectric therapies, have high recurrence rates and suboptimal clinical efficacy. Preliminary evaluations of the therapeutic effects of human umbilical cord mesenchymal stem cells (MSCs) in melasma mouse models have shown that MSCs can significantly improve skin pigmentation, reduce malondialdehyde (MDA) levels indicating anti-aging effects, ameliorate skin inflammatory cell infiltration, and promote skin repair in these models. This study is a single-center, randomized controlled clinical trial aiming to build on previous experimental findings by combining MSCs with photoelectric therapy for the treatment of melasma. Patients will be divided into three groups of 10 each: Stem Cell Treatment Group 1, Stem Cell Treatment Group 2, and a Control Group. Group 1 will receive intravenous infusion of MSCs followed by multi-point injection into the melasma area in combination with 755nm picosecond laser treatment. Group 2 will receive multi-point injection of MSCs into the melasma area in combination with 755nm picosecond laser treatment. The Control Group will only receive 755nm picosecond laser treatment. Efficacy will be initially assessed based on parameters such as the Melasma Area and Severity Index (MASI), VISIA skin analysis, and patient satisfaction. The study aims to evaluate the efficacy and safety of MSCs combined with photoelectric therapy for melasma and to investigate the underlying mechanisms.