Objective To explore the effect of 755 nm picosecond laser combined with polylactic acid microneedle on MASI score and skin barrier function in patients with melasma. Methods A total of 152 patients with melasma admitted to our hospital from June 2023 to June 2025 were selected, and they were divided into group A and group B by the random number table method, with 76 patients in each group. Group A was treated with 755 nm picosecond laser, and group B was treated with 755 nm picosecond laser combined with polylactic acid microneedle. The MASI score, skin barrier function, aesthetic effect, clinical efficacy and adverse reactions were compared between the two groups. Results After treatment, the MASI score of group B was (10.58±1.15)points, which was lower than (13.94±1.45)points of group A (P <0.05). After treatment, the sebum content, stratum corneum hydration and transepidermal water loss in group B were better than those in group A, and the melasma area, EI and MI were lower than those in group A (P <0.05). The total effective rate of group B was higher than that of group A (P <0.05). There was no statistically significant difference in the incidence of adverse reactions between the two groups (P >0.05). Conclusion 755 nm picosecond laser combined with polylactic acid microneedle can effectively improve skin barrier function and skin quality in patients with melasma, eliminate pigment lesions, and enhance facial aesthetic effect, without increasing the risk of adverse reactions.