The double-wall steel box cofferdam at pier 9^# of Longxi Jialingjiang grand bridge was taken as an example to systematically study 3D simulation analysis method for steel box cofferdam design under complex hydrogeological conditions of the big drop in water level, the great change in river bed erosion and the rapid flow velocity. The research results show that the design scheme of the steel box cofferdam meets the requirements of the stability index under all working conditions, and the structural design is reasonable. Compared with 3 356 groups of measured data under the same working conditions, the average error of the calculation results of the 3D model is 3.37%, and the largest error is 29.85%. So the calculation results of the 3D model are accurate relatively, which can provide some reference for the research and application of similar projects.