The invention provides a vehicle tailgate structure optimization method based on a two-step improved PSO (particle swarm optimization) algorithm. The method comprises the following steps: determiningdesign variables from a finite element model of a vehicle tailgate structure and calculating response of the model at each sample point, and establishing a high-precision surrogate model between eachworking condition response and the design variables; establishing a target function for the optimization of the vehicle tailgate structure, and using the two-step improved PSO algorithm, namely, a constrained PSO algorithm to perform global search and local search at a constrained boundary for optimization to obtain the optimized vehicle tailgate structure. The method has the advantages that the problem of dependence of the PSO algorithm optimizing capacity on adjustment of control parameters is solved, the optimizing capacity of the PSO algorithm in optimization of the vehicle tailgate structure with complex constraints can be improved effectively, and an optimized design result of the vehicle tailgate structure is improved remarkably.