A periodic optimization method for a diffractive optical element includes converting coordinates of individual target spots of a target spot array into angular spectrum coordinates, selecting an initial period, calculating diffraction orders of individual target spots, rounding the diffraction order, calculating the coordinates of actual projection spots by using the rounded diffraction orders, calculating evaluation indicator of period optimization, adjusting the period, and repeating the steps, and comparing the evaluation indicators to determine an optimal period for the diffractive optical element. With the periodic optimization method, an actual spot array is made to match a target spot array to the greatest possible extent with a small amount of calculations, thereby improving the design quality and accuracy of a diffractive optical element.