The numeral calculations of laser action was carried out by using one-dimensional heat conduction model. Different polishing effect on polycarbonate surface with different values of scanning speed were compared on the condition that the range of the laser power density for polycarbonate polishing was in the order of 104 W/cm2. The results show that the optimal processing parameters are as follows: the defocusing amount is 5 cm, the peak power density is 3.1×104 w/cm2, and the scanning speed is 20 mm/s, and the surface roughness of the PC sample can decrease from 5 μm to 2 μm without deterioration. With the increasing of the times of laser scanning, the surface roughness of the sample further decreased, and reached the minimum value around 10 times. The study is helpful for reducing the roughness of the PC surface.