Abstract: In this paper,a co-simulation method combining Particle Swarm Optimization (PSO) algorithm used in Matlab and the CST studio suite software is put forward to solve the design problem of wideband microwave absorber based on a two-dimensional periodic array of microstrip lines. It can both expand the absorbing bandwidth and decrease the thickness of the absorbing material by setting different fitness function. And the results show that the bandwidth is 30% expanded as well the thickness is 15% decreased. The bandwidth can be targeted expanded at the low end or high end by adjusting the weights of the fitness function The optimization processed automatically. The optimization is easy to carry out and able to get satisfied results.