Abstract: In order to simulate the diffraction field of apertured beam more precisely,the higher-order field can simulate the diffraction field of apertured beam by an appropriate increase of the expansion order M as the propagation distance z decreases.For different values of the propagation distance z,the expansion order M can be chosen according to the inequality proposed.Taking the super-Gaussian beam as an example,numerical calculation is performed to illustrate the application of the theoretical formulations.The results obtained in this paper are useful for studying the propagation of optical beam diffracted by an aperture.