Objective：To explore the main risk factors of recurrent aphthous ulcer（RAV） by investigating its pathogenic factors. Meth－ods：Using the self-made questionnaire of RAU’s risk factors to do the investigation. The high-risk factors of RAU were screened out from all correlative factors by non-conditional logistic regression analysis. Results：The high-risk factors including chronic digestive system disease，mental pressure，liking spicy food，family history，constipation，calculus index，smoking index and liking acidic food were introduced in the regression equation. OR values and regression coefficient of smoking index factor and liking acidic food fac－tor were less than 1 and 0，respectiuely（P＜0.05）. RAU and smoking index showed a negative correlation（rs=－0.170，P=0.000） while RAU and calculus index showed a positive correlation（rs=0.133，P=0.000） based on Spearman rank correlation analysis. Conclusions：These pathogenic factors from high-risk to low-risk were chronic digestive system disease，mental pressure，liking spicy food，family history，constipation and calculus index. Smoking and liking for acidic food may be the protective factors of RAU.