The relativistic effect and wakefield effect on the propagation of an intense laser pulse in plasma are compared in the resonant and non-resonant cases in detai l. The effect of wakefield, which depends on the initial pulse shape and width, leads to the asymmetry of pulse self-phase modulation. In the long pulse limit, the wakefield effect is negligible compared to the relativistic effect; in the short pulse limit, it balances the relativistic effect. Under the resonant cond ition, most of the photons within the pulse decelerates.