Focused on the scheme of the multi-color and multi-central frequency smoothing by spectral dispersion, the effects of the main parameters on the target uniformity are numerically simulated and analyzed, including the multi-color wavelength difference, the multi-central frequency wavelength difference, the bandwidth and the number of color cycle. And then, the parameters are further optimized. The results show that the target uniformity is first improved and then degraded with the increase of the multi-color wavelength difference, which means that there is an optimized multi-color wavelength difference. When the multi-central frequency wavelength difference and the bandwidth increase, the target uniformity is improved. However, neither of these two parameters could be too large since they are limited by the high efficiency of the third harmonic generation. For the given grating dispersion, the contrast of far field first decreases and then increases with the increase of the color cycle number. Therefore, the optimization is required under further analysis. The preliminary analysis indicates that the best color cycle number is not just to be one any more and changes with the parameters of the laser source and the grating.