During the car body painting process, the car body is prone to deformation after being subjected to shock loads from electrophoresis fluid. The traditional solution is to adopt multiple rounds of test testing to verify the feasibility of the scheme and conduct an optimization plan attempt, undoubtedly requires a long period of time and a large amount of human and material resources. The multi-phase flow simulation method and overlapping mesh technology are used to simulate car body electrophoresis process, extract the electrophoresis shock load of the body, simulate the deformation of the body through the simulation method, and optimize the overall structure through the topology simulation method to reduce the deformation during the electrophoresis process. The simulation method is in good agreement with the test results, and can be used to simulate, predict and optimize the deformation of car body structure during the electrophoresis process in the product design and development stage.