Abstract: In order to ensure the safety of people's lives and property, the flood prevention water level of west extension project of Beijing rail transit airport line is analyzed. The traditional hydrological analysis is used to calculate the maximum amount and ponding time in the project area.According to DEM topographic data, ArcGIS software is used to draw the range and depth of water accumulation in each drainage area with water balance method. The results show that under the condition of 50 year frequency rainfall, there is no water in Beixinqiao Station and Dongzhimen Station, and the lowest points of related engineering facilities are 0.26 m and 2 m higher than the surrounding water level, respectively. Therefore, under the design drainage standards, the construction project basically has no risk of waterlogging, and the impact of flood on the construction project is small. In addition, combined with the hydrological calculation and analysis of the basic situation of Tonghui River, the 100 year frequency flood water level is 0.36 m lower than the elevation of the dike top, therefore, the project is not affected by the 100 year frequency flood of Tonghui River.