A multi-central frequency and multi-color smoothing by spectral dispersion (SSD) scheme is presented for better beam smoothing than conventional SSD. One of the difficulties in conventional SSD is the narrow bandwidth limited by efficiency frequency conversion. The new scheme has overcome this problem by using multi-central frequency laser sources and a multi-color beam smoothing system. The multi-central frequency laser sources are incoherent combinations of several pulses in the time domain, each with different central frequencies and independent sinusoidal frequency-modulated components. Then, the laser beams from the multi-central frequency laser sources transmit in the multi-color smoothing system, spatially separated and independently spectrally dispersed by gratings array, independently achieve the third harmonic generation in KDP array with independent phase-matching for efficient conversion. Moreover, by adjusting the dispersion direction of the gratings to be perpendicular to each other, it is an effective way to achieve a 2D beam smoothing effect on the focal plane. Simulation results show that the novel beam smoothing scheme performs better than the conventional SSD.