Objective To compare the efficacy and safety of poly-L-lactic acid and hyaluronic acid injection therapy in improving facial depression and laxity. Methods A total of 70 patients with facial depression and laxity admitted to Suzhou Industrial Park Shengmei Medical Aesthetic Clinic from September 2023 to May 2026 were selected as the research subjects. According to the random number table method, they were divided into the control group (35 patients, treated with hyaluronic acid injection) and the observation group (35 patients, treated with poly-L-lactic acid injection). The facial laxity (FLR score), wrinkle severity (WSRS score), skin elasticity (R2 value), dermal thickness, subjective satisfaction (FACE-Q score) and complication rate were compared between the two groups. Results After treatment, the scores of FLR and WSRS in the observation group were lower than those in the control group (P <0.05). After treatment, the R2 value and dermal thickness in the observation group were higher than those in the control group (P <0.05). After treatment, the FACE-Q score of the observation group was higher than that of the control group (P <0.05). The incidence of complications in the observation group was 5.71%, which was lower than 22.86% in the control group (P <0.05). Conclusion Poly-L-lactic acid achieves better effects in improving facial depression and laxity than hyaluronic acid, with higher patient satisfaction and treatment safety, which is worthy of clinical application.