In order to study the pyrolysis of composites, an experimental investigation of carbon fiber reinforced epoxy resin composites was carried out. The samples, protected by tangential nitrogen flow, were subjected to a lower power density laser. The influence laws of laser irradiation time and power density on the pyrolysis of composites were obtained and discussed. The results reveal that, along with the laser irradiation time increase, the mass loss of samples increases monotonically while the thermal ablation rate of samples decreases gradually and will tend to be steady. On the other hand, the mass loss of samples is proportional to the laser power density. However, the thermal ablation rate increases significantly at first along with the power density increase, and then slowly since it enters into the glacis.