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CFD analysis and multi-parameter multi-objective optimization method is used to study the aerodynamic design on the air deflector of a van-body light duty truck.The process starts with a shape parameterization of the air deflector,and then selects eight factors representing the characteristics of the air deflector.Adaptive sampling method is used to fill the sample space because of its characteristic of reducing the number of solutions.After that the approximate model is established.The optimization goal is getting minimum value of Cd(vehicle aerodynamic drag coefficient).Finally,the global optimization is performed by using the multi Island genetic algorithm.After optimization,the optimized design can result in a 13.6% reduction in Cd compared to the truck that matched the original air deflector.In addition,Pareto front line is introduced to find the optimal matching of all these parameters considering simultaneously the Cd and the weight of air deflector.According to the results,designers can consider the two factors to choose the best model.