Objective The model of oral ulcer in rats was constructed by areca nuts extract, and the structural changes and diversity characteristics of oral flora were observed, so as to explore the pathogenesis of oral flora involved in oral ulcer in rats induced by areca nuts extract, providing theoretical support for clinical prevention and treatment of oral ulcer. Methods Thirty SD rats were randomly divided into normal group, model group, drug treatment group, 10 rats/group. The rat oral mucosa was injected with 10g/mL areca nuts extract subcutaneously to replicate the rat oral ulcer model. Ulceration area, ulceration score, and levels of TNF-α, IL-2, and IL-8 in local tissues were observed, and HE staining was performed on oral mucosal tissues to observe the morphological changes of oral mucosal tissues. High-throughput sequencing method was used to analyze the structure distribution of oral microbial flora and microbial community diversity. Results Compared with normal group, the ulcer area of rats in model group was significantly increased (P<0.01), the ulcer score was significantly increased (P<0.01), the levels of IL-2, IL-8 and TNF-α in oral mucosal tissue were significantly increased (P<0.01), and the shannon index of oral saliva of rats was significantly increased (P<0.05).simpson index was significantly decreased (P<0.01), Strep-tococcus and Veillonella were significantly decreased (P<0.05,0.01), oral mucosal epithelial cell proliferation or focal necrosis, mucosal lamina propria edema and hemorrhage were observed in model group. It was accompanied by abundant infiltration of neutrophils and monocytes. Compared with model group, the ulcer area and ulcer score of model group were significantly decreased (P<0.05), the levels of IL-2, IL-8 and TNF-α in oral mucosal tissue were significantly decreased (P<0.05,0.01), and the shannon index of oral saliva of rats was significantly decreased (P<0.05). Simpson index was significantly increased (P<0.01), Strep-tococcus was significantly increased (P<0.001), Staphylococcus was significantly decreased (P<0.01), and the pathological degree of oral mucosa was significantly improved. Conclusion Areca nuts extract can successfully reproduce the rat model of oral ulcer, and it is speculated that the development of oral ulcer disease induced by areca nuts extract may be related to the imbalance of oral flora and local tissue inflammatory mediators.