Abstract: A modified iterative algorithm based on phase mixture was put forward in designing diffractive optical elements, aiming at recovering diffractive patterns of the output beam precisely. Different from Gerchberg-Saxton algorithm, in this paper, the new phase initiation was set as the weighted sum of the two phase functions in the succeeding neighbor loops to be immune from trapping local minimum. The formulas for calculating phase factor were given, and the selection of phase factor was discussed. The beam transformations from Gaussian distribution to uniform and to annular distribution were exampled to investigate with Gerchberg-Saxton algorithm and the proposed algorithm. The numerical result demonstrates a nearly uniform and annular target profile, and the ultimate mean square error, top beam uniformity, and energy efficiency of the proposed algorithm were all more excellent than Gerchberg-Saxton algorithm. This work can obtain better output diffraction pattern, and has reference value for the design of diffractive optical elements.