In this work, the effect of temperature on the microstructure evolution of vacuum brazed joint of TiAl alloy and 42CrMo was studied. The results have shown when the brazing temperature is under 870 degrees C, no compound is formed at the boundary on the 42CrMo side. But when brazing temperature is over 870 degrees C, a very narrow TiC compound film is found at the homologous site, while on the TiAl side, there always exists a Ti(Cu,Al), intermetallic compound layer at any brazing temperature. The elemental diffusion and reaction is the predominant factor of joint forming. The tensile fracture strength of brazed joint increases with the brazing temperature, the increase of the tensile strength of joint is due to the variation of the joint structure.