In typical techniques of smoothing by spectral dispersion (SSD), illumination uniformity cannot be further improved by increasing the pulse bandwidth due to the limitation of high-efficiency frequency tripling. Combined with the analysis of the schemes of four-color beam smoothing and multi-frequency modulator SSD, a novel scheme of beam smoothing using multi-central frequency and multi-color smoothing by spectral dispersion has been proposed, which not only can achieve high-efficiency frequency tripling, but also can obtain laser beams with nearly continuous spectrum and exhibit some specific advantages in far-field smoothing. Results show that the focal spot will be enlarged slightly but obviously further smoothed by the use of the new scheme. Compared to the typical SSD technique, the new scheme can decrease hot spots effectively and achieve the best irradiation in less time. Moreover, with independent combination of dispersion directions in each quadrant of grating array, a multi-dimensional smoothing on focal spot can be realized.