A theoretical model to analyze the beam smoothing performance,realized by the diffractive optical element (DOE) and the smoothing by spectral dispersion (SSD) technique,is setup based on the spatial frequency spectra analysis method. Utilizing this theoretical model,the parameters,including the integration time,the modulation frequency,the phase modulation coefficient and the linear dispersion of the diffraction grating,of the SSD technique can be optimized to improve the beam smoothing performance. The influences of the parameters of the SSD technique on the beam smoothing performance are numerically analyzed. Furthermore,the simulated results show that the phase distortion should be changed during the integration time in order to obtain a good beam smoothing performance.