It is to summarize Professor DAI Yongsheng's clinical experience in the treatment of recurrent aphthous ulcers, and expound the etiology and pathogenesis of spleen and stomach Qi deficiency resulting in heart and kidney fire.Professor DAI Yongsheng believes that the occurrence of recurrent aphthous ulcers is related to the five internal organs.According to the clinical experience of the five elements of syndrome differentiation and treatment of recurrent aphthous ulcers, combined with the theories of traditional Chinese medicine, including the tongue is "heart seedling", "the spleen is open to the mouth, its Hua is in the lips", "the kidney is licking the tongue", he believes that recurrent aphthous ulcer is closely related to the decline of spleen and stomach function as well as heart and kidney fire.Among them, "the etiology and pathogenesis of spleen and stomach Qi deficiency resulting in heart and kidney fire" is one of the important pathogens of DAI's syndrome differentiation for recurrent aphthous ulcer, which is the result of years of experience in clinical trials. "Tuxu" means spleen and stomach Qi deficiency and the "fire upward" includes three parts: one refers to the fire in the spleen and stomach, the second refers to heart fire floating up, the third refers to kidney fire floating up.The method of supplementing the common soil to put down the fire is effective.Therefore, this article intends to provide a more reliable theoretical basis for the treatment of recurrent aphthous ulcers in the future by studying Professor DAI Yongsheng's flexible use of TCM classic knowledge to guide the clinical syndrome differentiation.