Experimental research on 1.3 μm reflectance of epoxy/organsilicone two-layer composite coating under infrared continuous-wave (CW) laser irradiation in vacuum is carried out. An experimental system for laser irradiation and reflectance measurement is set up with conjugated reflectometer. Results of signal detection theory (SDT) analysis indicate that heat deposition generated by laser makes pyrogenation of epoxy primer which leads to form and burst of bubbles and thermal ablation of topcoat. Heat transfer within coating-metal structure is simulated by finite element analysis procedure with interface thermal resistance modification, and the temperature-dependent reflectance is presented. Investigation results show that the change of reflectance is related to the modes of damage and processes of decomposition. 1.3 μm reflectance of epoxy/organsilicone coating is about 0.80 at room temperature, changes slightly at the very beginning of laser irradiation, decreases remarkably while bubbles burst and thermal ablation occurrs, and finally maintains a rather low level. There are three characteristic temperatures of reflectance evolution, the decomposition temperature of epoxy primer, the decomposition temperature of organosilicone topcoat, and the decomposition temperature when the reaction ends and the surface tends to be steady.