Abstract: The ICF system has strict requirements on the focal spot size and intensity distribution uniformity during the design process of continuous phase plate(CPP). The relationship between CPPs surface and the light intensity uniformity of far field focal spot is studied, and the influences of CPPs surface modulation depth on the size of focal spot are analyzed and calculated theoretically. Results show that the growth of the radius of focal spot is in direct proportion to the increase of the surface modulation depth of CPP. For the sake of random behavior of CPP, the difference of far field characteristics between CPPs is compared, and the influences of modulation depth on the peak-valley and root mean square value of light intensity are studied, which shows that the differently designed CPP has different behavior in far field. When the modulation depth is around 5 to 15, the focal spot could have a relatively low peak-valley and low root mean square value, which means that the CPP is in good smoothing performance.