Abstract: In order to improve the design safety of gravity dam and avoid excessive capital investment and waste, it is very important to choose a reasonable debris flow impact as the design basis. This paper takes Sanyanyu ditch debris flow disaster prevention and control project as the background, based on ABAQUS, to calculate limit resistance analysis on gravity dam of Sanyanyu ditch debris flow. The numerical method of increment loading is used to evaluate the lateral impact resistance of gravity dam under two working conditions. According to the feedback from the Sanyanyu prevention and control project, it is proved that the average value of working conditions 1 and 2 of impact force selection is reasonable in the design of debris flow control project, and it is explained that the method is used in combination with the empirical formula, and the results are more accurate and reliable. It has good application prospect in debris flow engineering design and research.