Femtosecond laser processing has the characteristics of short pulse, high peak power, and small heat-affected zone. Even so, there is still a heat accumulation in the material removal process. The heat accumulation between pulses has a direct impact on the processing quality and the heat-affected zone. In this paper, carbon fiber reinforced resin matrix composites (CFRP) are ablated by femtosecond pulsed laser, and a three-dimensional heat transfer model is used to study the temperature field of the pulsed spot, and then the thermal accumulation effect of the femtosecond laser is discussed. The results show that the pulse energy and repetition frequency have a significant influence on the heat accumulation; the calculated results of the 3D heat transfer model are basically consistent with the experimental results. This 3D heat transfer model can provide references for the control of the heat accumulation effect in femtosecond laser processing of CFRP materials.