The physical content of smoothing by spectral dispersion (SSD) technology is theoretically explained that the focal spot smoothing effect of SSD results from the temporal change of the far-field primitive electric field phase, and there is no physical image of "moving" focal spot in the practical application of SSD. On this basis, the theoretical model of "intensity sweep" laser beam, which has a far-field intensity distribution with constant form but temporal changed spatial position, is established. The smoothing characteristics of the beam are studied by numerical simulation compared with that of SSD.