Abstract: In order to analyze the temperature of TC4 titanium alloy/carbon fiber reinforced thermoplastic composite(CFRTP)stack structure and its influence during friction lap joining (FLJ), a 3D geometric model considering the frictional heat source was established.Through simulation using ABAQUS software, the temperature field and thermal cycle curve during FLJ process were obtained, and the influence of rotational speed and welding speed on the temperature field were analyzed.The FLJ tests of TC4/CFRTP were carried out, and the effect of temperature change on the welding defects was analyzed through the microstructure observation of the connection area.The results show that the model can quickly and accurately simulate the temperature field of TC4/CFRTP during FLJ process.The bigger the rotational speed and the smaller the welding speed, the higher the temperature of the connection area.Excessive temperature causes thermal degradation of the CFRTP’s thermoplastic matrix, and the pyrolytic gas that is not discharged in time will form bubbles in the connection area, and the number and size of pores increase with the temperature increasing.