The　characteristics　of　temperatures,　stresses　and　strains　fields　have　been　studied　numerically　for　a　titanium　alloy　sheet　welded　with　an　improved　gas　tungsten　arc　welding　method,　in　which　a　trailing　spot　heat　sink　is　introduced　to　control　the　welding　stress　and　distortion.　The　impinging　jet　model　is　employed　to　describe　the　intense　heat　transfer　between　the　cooling　media　and　the　top　surface　of　the　workpiece.　The　influence　of　the　distance　between　arc　and　heat　sink　is　investigated.　Results　show　that　there　is　an　ideal　range　of　distance.　Using　the　ideal　distance,　a　low　stress　and　no　distortion　welding　structure　can　be　derived.