Abstract: It was discussed whether the unloaded behavior was existed in welding cooling process or not, and the welding stress and strain of titanium alloy welded with moving arc were simulated. The welding thermal elsto-plastic stress-strain cy cle of titanium alloy was presented quantitively.The results showed that there is unloaded behavior in welding cooling process of titanium alloy.The welding thermal elsto-plastic stress-strain cycle of titanium alloy is composed of molten pool, compressed plastic zone, tensile plastic zone, unloaded zone and compressed elastic zone.Weld and the zone nearby constitute the tensile plastic zone which is lolcated in the mechanical molten isotherm.At the residual state, weld and the zone nearby are in the unloaded state.