In order to reduce the water contamination on side window of vehicle running in the rain and improve driving safety，an water contamination optimization design of side window was carried out based on the boundary seeded domain method and automatic optimization design method． The parameters of the A-pillar section were se-lected as design variables，and the sample space was constructed using orthogonal test design． The droplet trajec-tory and water covering area on side window were calculated by combing lattice Boltzmann method，the Lagrangian particle motion model，the liquid film model and boundary seeded domain method． The approximate relationship between the design variables and the contaminated area was fitted by the Kriging model． Multi-island genetic algo-rithm was used to get the minimum area of side window water contimination． The results show that the area of water contamination in the side window of the optimized model decreases by 66. 2%．