Abstract: Based on SYSWELD software, Satoh Test of 9Cr-1Mo steel was simulated and the temperature-stress curves under different conditions were obtained. Using the simulated results, we discussed the influence of volume change, yield strength variation and phase transformation induced plasticity (TRIP) on the formation of residual stress. Meanwhile, the welding residual stresses induced by TIG welding process in 9Cr-1Mo steel joint was simulated using the developed computational approach. Simulation results show that volume change during austenite-martensite phase transformation has a significant influence on the formation of welding residual stresses, and it not only changes the magnitudes of residual stress but also even can alter the sign of residual stress. Yield strength variation also has certain influence on welding residual stresses. Comparing with volume change and yield strength variation, TRIP seems has less influence on welding residual stress, however, it can relax stresses during phase transformation in the fusion zone and the heat-affected zone.