As a typical coastal city, Sanya frequently suffers from typhoon, heavy rain and storm. Compared with the cities in inland area,the factors of flood disaster in Sanya are more complex and the influences are more serious.The paper built a storm, flood, tide multiple coupling numerical model based on high precision DEM data,precisly restored the main boundaries,and used partition roughness to reflect the impact of different dowm face,and used wet-dry theory to deal with variable boundary.This paper got the point of flood disaster,depth of water and influence factor in main suburb of Sanya.The result has importment real significance for the scientific guidance, risk management of flood disaster in Sanya.