Abstract: In this paper,a constrained optimization method is adopted to design diffractive optical elements.As an example,a Dammann gratings design method with adaptive particle swarm optimization is proposed.The algorithm could not only guarantee convergence to global optimum,but also improve convergence rate and the solution quanlity.And in the algorithm,a penalty function is introduced,which can balance the relation between the high uniformity and the diffraction efficiency.A dammann gratings with 15 uniform spots are designed by using the proposed algorithm,the simulation results show that the proposed algorithm can obtain reasonable convergence speed and reasonable uniformity with given an expected diffraction efficiency,and the intensity uniformity can reached 10^-5order.