Abstract: Now, the optimization algorithm with electromagnetic simulation software HFSS are often combined to design the microstrip antennas. However, a large number of accurate electromagnetic simulations are very time-consuming and need high performance computer. In order to solve the problem, a method, which replaces full-wave electromagnetic simulation with Gaussian process modeling and then optimizes with the particle swarm optimization(PSO) algorithm, is proposed. The method can reduce the time to 0.2% of the previous method. The method is used to optimize the GPS dual-mode microstrip slot antenna(MSA). The optimal results of GPS dual-mode MSA satisfy the design demands which proves the effectiveness of the method.