Abstract: The post-welding heat treatment(PWHT) is simulated by finite element method.The results show that large as-weld residual stress is generated in the weld metal and heat-affected zone(HAZ),and is decreased gradually far away the HAZ.After PWHT,the residual stress is decreased about 60%.PWHT not only decreases the residual stress,but also makes the residual stress re-distributed.The stress re-distribution makes the stress in base metal increase.During the heating of PWHT,the yield strength is decreased and the plastic deformation is generated,which leads to the relaxation of residual stress.During the cooling of PWHT,the yield strength is increased,which makes the stress increase.The residual stress after PWHT is mainly generated during the cooling of PWHT.The maximum residual stress is increased with the PWHT temperature increase,but keeps stable above 600℃.Therefore a suitable temperature of 600℃ could be used in PWHT for Q345R steel.