Abstract: Particle swarm optimizers (PSO) are combined with finite element method to optimize plate structures with discrete variables. The mapping function method is used to range the discrete variables and a sequential numbers is obtained. Thus, the searching for discrete variables is replaced by searching the sequential numbers of the discrete variables. Therefore a discrete optimization problem is converted into a continuous optimization one. The calculation module for plate optimal problem is developed with particle swarm optimizers based on finite element method. Three different optimizers are applied to three optimal design examples, showing the proposed method is feasible and the heuristic particle swarm optimizer (HPSO) is the most efficient method.