Objective To investigate the clinical efficacy of ultrapulse carbon dioxide fractional laser (UCFL) plus subcision on depressed scars after acne. Methods 92 patients with acne scars admitted in our hospital from March 2016 to September 2018 were divided into observation group (n=46) and control group (n=46) on the basis of random number table. The control group was administrated with UCFL (3 times, once a month), while the observation group subcision 2 weeks later than UCFL skin renewal. The clinical efficacy was assessed 3 months after the treatment. Changes of patient self scoring and physician visual scoring at different timings after treatment, changes of clinical acne scar assessment scale (ECCA) weighted scores and p38 mitogen activated protein kinase (p38 MARK) related protein level before and after treatment, as well as occurrence of side effect were compared between the two groups. Results The total effective rate of the observation group (95.7%) was significantly higher than that of the control group (82.6%) (P < 0.05). At the end of 3 months after treatment, the ECCA weight scores of the two groups were significantly lower than before treatment, and the observation group was significantly lower (P < 0.05). The self score and physician visual score of the two groups increased with the increase of treatment times, and the observation group were significantly higher than the control group at the same time (P < 0.05). At the end of 3 months, the concentrations of MAPK kinase 1, 2 and extracellular signal regulated kinase-1, 2 in the two groups were significantly lower than those before treatment, and the serum levels of p38 MAPK signal pathway related proteins in the observation group were significantly lower than those in the control group (P < 0.05). The treatment-related adverse events in both groups were transient symptoms, which could recover by themselves, and no other serious side effects were found. Conclusion The overall effect of ucfl combined with subcutaneous separation in the treatment of post acne sunken scars is accurate, which is helpful to improve the appearance of patients with acne sunken scars. The mechanism may be related to the significant positive regulation of p38 MAPK signal transduction pathway by the combined therapy.