To improve the numerical simulation accuracy of carbon fiber reinforced thermal plastic (CFRTP)/stainless steel laser direct joining (LDJ), a fitting formula of thermal contact conductance is established based on the experiments. Taking the thermal contact resistance into account, we establish a three-dimensional finite element thermal contact model of LDJ. The theoretical simulation and experimental results are compared and analyzed. The results show that the thermal contact model is more consistent with the reality compared with the traditional model. Therefore, the thermal contact model can be used to characterize the influence of clamping pressure on the laser joining quality. When the laser power is 339 W and the clamping pressure is 0.1 MPa, the relative error is 12.3% for the traditional model and it is reduced to 2.8% for the thermal contact model. The numerical model can help to improve the accuracy of numerical simulation in the process of LDJ and choose optimal technological parameters.