The finite element method is applied to calculate the welding residual stress for Invar steel of a liquefied natural gas (LNG) carrier’s containment system, whereas the x-ray diffraction method is applied to measure the longitudinal welding residual stress of the welding joint. The calculation and measurement results indicate that the measurement results of longitudinal residual stress are lower than the calculation results, but the distribution of both results is consistent with each other. The measurement results indicate that the longitudinal residual stress near the welding seam increased first and then decreased with the increasing distance to the welding seam, and the tensile residual stress converted to the compressive stress gradually. There exists high longitudinal residual stress in the weld seam and the heat-affected zone of Invar steel, and the maximum residual stress is above 200MPa, which may decrease the fatigue life of Invar steel. Thus, the influence of welding residual stress cannot be neglected when you assess the fatigue life of a LNG carrier’s containment system under the sloshing impact.