Abstract: The diffraction and near-field-intensity smoothing characteristics of periodic chirp pulse after spectral dispersion in the laser driver of inertial confinement fusion are analyzed theoretically and simulated numerically, and the effect of color cycles on the both is calculated. The calculation results indicate that the far field increases and intensity modulation is enhanced with the increase of color cycle; the near-field-intensity smoothing effect becomes better but the spatial shape distortion is enhanced along with the increasing of the color cycles and propagation distance. And through smoothing effect comparison, periodic chirp pulse is found to be better than the sinusoidal phase modulated laser beam on the smoothing of near-field-intensity.