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　cycle　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.