[Objective] The flood disaster in small watershed of island areas was simulated, in order to provide technical support for the subsequent development and construction of island areas and the smooth development of flood prevention and drainage management.[Methods] Taking Zhujiajian Island in Zhoushan City of Zhejiang Province as the research object, MIKE was used to establish a one-dimensional river network model, a two-dimensional hydrodynamic model and a coupling MIKE FLOOD model based on the data of design rainstorm, and the design and check tide level. The inundated area and the inundated water depth of the study area, the water level of the main river section, and the inundated duration of the key study area under these two schemes were compared and discussed.[Results] Compared with Scheme 1 (94 rainfall + measured tide level) under the condition of designed rainstorm and tide level, the inundated area of Scheme 2 (94 rainfall + extreme tide level) under the condition of design rainstorm and check tide level was larger and the maximum inundated water depth of the latter was deeper at the relatively high water level.[Conclusion] The flood control ability of Zhujiajian watershed caused by rainstorm is weak because of the large gradient ratio of rivers, the short confluence time, poor regulation and storage capacity. Especially when the rainstorm suffers astronomical spring tide, the disaster degree of the study area will be more serious.