Abstract: The distributions of longitudinal residual stress and longitudinal residual plastic strain of titanium alloy Ti-6Al-4V thin plate welded by conventional GTAW and GTAW with a trailing heat sink (DC-LSND) were studied experimentally using "Slot-sectioning stress relaxation" method.The experimental results showed that the maximum residual tensile stress in the weld with conventional GTAW is 45% of the yield strength of the titanium alloy.Because of the extremely-high gradient cooling of the heat sink in DC-LSND GTAW,high tensile effect acts on the zone between the arc and the trailing heat sink,the tensile plastic strain is produced,which compensates some portion of the longitudinal incompatible strain cause by arc heat source.Therefore longitudinal residual plastic strain,the maximum residual tensile stress and residual compressive stress are reduced properly.