Objective To explore the effect of red and blue light combined with ultra-pulsed fractional CO2 laser on scar repair in patients with moderate to severe acne vulgaris. Methods A total of 80 patients with moderate to severe acne vulgaris admitted to the Department of Dermatology and Venereology, Liyang People's Hospital from September 2024 to March 2025 were selected as research subjects, and they were divided into group A and group B by the random number table method, with 40 patients in each group. Group A received conventional drug treatment, and Group B received red and blue light combined with ultra-pulsed fractional CO2 laser on the basis of group A. The scar repair, clinical efffcacy, inffammatory lesion counts and adverse reaction rate were compared between the two groups. Results After 12 weeks of treatment, the ECCA scar score in group B was lower than that in group A (P<0.05). The total effective rate of group B (92.50%) was higher than that of group A (75.00%) (P<0.05). The inffammatory lesion count in group B at 4, 8 and 12 weeks after treatment was lower than that in group A (P<0.05). There was no signiffcant difference in the incidence of adverse reactions between the two groups (P>0.05). Conclusion For patients with moderate to severe acne vulgaris, red and blue light combined with ultra-pulsed fractional CO2 laser can reduce inffammatory lesion count and improve scar, with good efffcacy and equivalent safety.