Based on the Fourier heat exchange equation, the heat-damage model irradiated by continuous-wave laser is developed on the basis of considering the phase transition of the material. Using the model, the temperature field in 30CrMnSi steel substrate that coated by polycarbosilane (PCS) composite coating are analyzed. And the effects of laser parameters and coating thickness on the temperature field are discussed too. The calculation results agree well with the experimental results, which can provide the theoretical basis for analyzing the laser ablation effect of laser protection material, such as PCS. The simulation results demonstrate that, the PCS composite coating provides obvious thermal protection to the 30CrMnSi steel substrate and the laser-to-target power density of continuous-wave laser has more sensitive influence on the PCS laser-proof effect.