Objective To investigate the effect of collagen repair on the width and thickness of keratinized gingival in patients with dentition defect and moderate to severe oral soft tissue defect. Methods A total of 62 patients with dentition defect and moderate to severe oral soft tissue defect admitted to Guangxi Honorary Soldiers Rehabilitation Hospital from July 2022 to June 2023 were selected, and they were divided into the reference group and the experimental group according to different repair methods, with 31 patients in each group. The reference group received free gingival graft repair, and the experimental group received collagen repair. The width and thickness of keratinized gingival, oral health indicators, clinical efficacy and adverse reactions were compared between the two groups. Results At 6 months and 1 year after operation, the width and thickness of keratinized gingival in the experimental group were higher than those in the reference group (P<0.05). There were no significant differences in the MPI and MBI between the two groups (P>0.05). At 6 months and 1 year after operation, the BOP and PD in the experimental group were lower than those in the reference group (P <0.05). The total effective rate of treatment in the experimental group (90.32%) was higher than that in the reference group (67.74%) (P <0.05). The incidence of adverse reactions in the experimental group (6.45%) was lower than that in the reference group (29.03%) (P <0.05). Conclusion The effect of collagen repair in patients with dentition defect and moderate to severe oral soft tissue defect is better than that of free gingival graft repair, which can increase the width and thickness of keratinized gingival, maintain oral health, and reduce the incidence of adverse reactions.