Objective To explore the effect and safety of poly-L-lactic acid (PLLA) injection on improving facial depression and laxity. Methods A total of 60 patients with facial depression or laxity who visited Beijing Badachu Second Medical Cosmetic Hospital from October 2023 to April 2024 were selected, and they were divided into the control group and the study group by the random number table method, with 30 patients in each group. The control group was given hyaluronic acid injection filling treatment, and the study group was given PLLA injection treatment. The facial laxity and wrinkle severity, subjective satisfaction and skin elasticity parameters were compared between the two groups. Results The facial laxity scores and wrinkle severity scores of the study group at 1, 3, 6 and 12 months after treatment were lower than those of the control group (P <0.05). The subjective satisfaction scores of the study group at 1, 3, 6 and 12 months after treatment were higher than those of the control group (P <0.05). The R2 and R7 of the study group at 1, 3, 6 and 12 months after treatment were higher than those of the control group (P <0.05). Conclusion PLLA injection can effectively improve facial laxity and wrinkles, enhance patients' subjective satisfaction and skin elasticity, which is worthy of clinical application.