The MSC Marc software is used to establish the thermal-mechanical coupled finite element model to analyze the evolution of temperature and stress deformation during laser direct deposition. Considering the stress relaxation behavior of titanium alloy at high temperature, the material constitutive equation is modified through several iterations. At the same time, based on the thermocouple and laser displacement sensor, a transient real-time measurement device is developed to measure the temperature and deformation of titanium alloy thin-wall parts during the actual forming process. By comparing and analyzing the simulated and measured values of the modified model, the results show that the temperature error between the in-situ measurement results and the simulated results is only 7.9%, the deformation error is 19.6%, and the laws of the substrate deformation are consistent. The stress in the deposition layer is generally tensile, and the main stress direction is consistent with the deposition direction.