Abstract: The welding temperature field, the distributions of residual stresses as welded (AW) and electron beam local post-weld heat treatment (EBLPWHT) of BT20 plates have been successfully simulated with a three-dimensional finite-element model(FEM). In the weld center, the maximum magnitude of residual tensile stresses of BT20 thin plates of titanium alloy is equal to 60%~70% of its yield strength σ_s. The residual tensile stresses in weld center can be even decreased after EBLPWHT and the longitudinal tensile stresses are decreased about 50% compared to the joints in AW conditions. The numerical calculating results of residual stresses by using FEM are basically in agreement with the experimental results. Combined with numerical calculating results, the effects of electron beam weling on the distribution of welding residual stresses in thin plates of BT20 has been analyzed in detail.