The design of flood water surface profile calculation is the core work of river regulation projects. In this paper, the central urban area of Leshan was taken as the research object. The Wutongqiao station downstream of the confluence of the Min River, Dadu River, and Qingyi River was selected as the flood control section. The flood composition of the three rivers was calculated using the typical year flood composition method. The roughness was determined using the measured flood process and flood trace investigation. The outer line of different water surface profiles was taken as the result. The results show that the typical year combination method uses the actual flood composition as a sample for flood allocation, which is simple and easy to implement. Multiple typical years can more comprehensively reflect the characteristics of regional flood composition, which is suitable for the calculation of the design flood water surface line in areas with complex flood composition.