Objective To study the clinical effect of vitamin C combined with gentamicin sulfate in the treatment of recurrent oral ulcer. Methods A total of 86 patients with recurrent oral ulcer who were treated in Penglai Hospital of Traditional Chinese Medicine of Yantai from August 2019 to June 2021 were selected as the research objects. According to the random number table method, they were divided into routine group and combined group, with 43 patients in each group. The routine group was treated with basic treatment, and the combined group was treated with vitamin C combined with gentamicin sulfate. The clinical treatment effect and the level of inflammatory factors were compared between the two groups. Results The total effective rate of clinical treatment in the combined group was 95.35%, which was higher than 79.07% in the routine group (P <0.05). After treatment, the levels of hs-CRP, IL-6, IL-17 and TNF-α inflammatory factors in the two groups were lower than those before treatment, and those in the combined group were lower than those in the routine group (P <0.05). Conclusion Vitamin C combined with gentamicin sulfate in patients with recurrent oral ulcer is beneficial to improve the clinical treatment effect and reduce the level of oral infection and inflammatory response, which is worthy of clinical application.