Abstract: Based on the smooth particle hydrodynamics method, a rain simulation model of the front windshield lower trim panel system was established in AVL PreonLab simulation software, and it was found that the risk of air conditioning inlet and wiper motor is low risk under the original scheme, but the risk of water in the cabin is greater. Considering the weakening of the sealing effect after the durability of the sealing cotton, the water may flow into the cabin; secondly, the water barrier bars on both sides of the wiper cover are not wide enough in the Y direction, and the water will flow into the cabin when the rain is heavy. Through the simulation analysis of the optimization scheme, the problem of water in the cabin can be solved, and the problem can be found in advance at the design stage, and the optimization scheme can be proposed to reduce the development cost of the whole vehicle, which is an important guidance for the development of water management of the whole vehicle.