Abstract： Objective： To observe the clinical effect of Qushi Xiegan Jiedu Decoction combined with western medicine on post-adolescent moderate to severe acne with damp-heat accumulation syndrome. Methods： A total of 118 cases of patients with post-adolescent moderate to severe acne with damp-heat accumulation syndrome，treated at the Department of Dermatology， Luoyang Branch of Dongzhimen Hospital Affiliated to Beijing University of Chinese Medicine from January 2022 to December 2023， were divided into the control group and the observation group according to the random number table method，with 59 cases in each group. Ultimately，55 cases in the control group and 56 cases in the observation group completed the study. The control group was treated with Isotretinoin combined with Minocycline Hydrochloride Capsules， and the observation group was additionally treated with Qushi Xiegan Jiedu Decoction on top of the control group's regimen. Both groups were treated for six weeks. The skin lesion status，levels of interferon-γ （IFN-γ） and interleukin-4 （IL-4），incidence of adverse reactions before and after treatment as well as the clinical effects and recurrence rates were compared between the two groups. Results： After treatment， the total effective rate in the observation group was 91.07% （51/56）， higher than 76.36% （42/55） in the control group （P＜ 0.05）. Traditional Chinese medicine syndrome scores in the two groups were decreased when compared with those before treatment （P＜0.05）， with the observation group showing lower score than the control group （P＜0.05）. Scores for papules，comedones，pustules，and seborrhea decreased in the two groups compared to before treatment （P＜0.05）， with the observation group showing lower scores than the control group （P＜0.05）. Levels of IFN-γ increased in the two groups compared to before treatment （P＜0.05）， with the observation group showing higher level than the control group （P＜0.05）；the levels of IL-4 decreased in the two groups compared to before treatment （P＜0.05），with the observation group showing lower level than the control group （P＜0.05）. The incidence of adverse reactions did not differ significantly between the two groups （P＞0.05）. Follow up for three moths，the recurrence rate in the observation group was lower than that in the control group （P＜0.05）. Conclusion：Qushi Xiegan Jiedu Decoction combined with western medicine is effective in treating post-adolescent moderate to severe acne with damp-heat accumulation syndrome， effectively reducing skin lesion status， improving clinical efficacy， reducing recurrence， and demonstrating good safety.