Transmission characteristics of smoothed beam spots near the focal plane were investigated under the influence of nonlinear intensity and phase modulation. Diffraction theory was used to calculate the light field distribution on the defocused surface in three-dimensional space. Spot position drift and intensity symmetry were used to characterize beam spot performance during transmission evolution. The impact of non-linear effects under high-flux laser irradiation on smoothed spot of continuous phase plate was studied. Especially, the small-scale self-focusing intensity modulation difference caused by large difference between the thick and thin ends of wedge lens resulted in gradual deviation of beam spot from the optical axis during the defocusing transmission process, and caused asymmetric bias of intensity distribution. The results show that the effect of nonlinear intensity distortion is far greater than that of phase distortion. Under irradiation with 5 GW/cm 2 power density on a given laser device, the spot position offset is more than 0.1 mm on the 4 mm defocused plane, and the asymmetry of light intensity is biased to 30%.