A fast and effective algorithm for designing the diffraction optical element (DOE) with a wide-diffraction angle is presented. DOE had been widely used in many fields in recent years, but there are finite methods which can design DOE with wide-diffraction angle quickly occupying a small quantity of computing resource. By the use of a nonparaxial scalar diffraction equation as the light transmission operator, a modified iterative algorithm is proposed. To verify our algorithm, the checkerboard image, binary image, and gray-scale image are numerically simulated, respectively. The simulation results show that the final variance between the preset image and final pattern is very small, the value is generally lower than 10−5, and the natural images even have a final variance less than 10−12. At the same time, the diffraction efficiency has been significantly increased to be larger than 90%, which indicates that the design method is effective and practical.