Abstract: Due to the premature convergence of PSO，immunity niche concept is adopted to improve the performance of PSO.Orthogonal principle is applied to the initialization of particle，so particles are evenly distributed.During the evolution，every particle is extended to a region by immunity operation，so the algorithm can improve the diversity and has the capability of avoiding premature convergence.Since the immunity operation is only performed every several generations，The convergence velocity is improved.And it is verified by Ackley function，Shcaffer function and Grievank function in MATLAB，the result shows that the improved PSO can realize global optimization effectively.