In order to predict and control the polymer temperature field of laser melting molding process, the finite element analysis model of CO2 laser scanning irradiation polymethylmethacrylate (PMMA) is built based on the principles of heat transfer and energy balance. Numerical simulation of the laser melting process of the sample is carried out at low power CO2 laser scanning irradiation, the effects of laser parameters such as laser power, scanning time, scanning speed and spot diameter on samples three-dimensional transient temperature field are investigated, and the intrinsic relationship between laser parameters and sample temperature is analyzed. Simulation results show that the highest temperature of the sample wavily increases and the minimum temperature linearly increases, the temperature difference increases with scanning time increasing, and the sample substrate can be controlled at softening temperature or melting range to select appropriate parameters of the laser. The simulation results are in good agreement with the experimental research of the laser melting and molding, which can provide a reference to study the mechanism of polymer laser melting and molding process embodiments.