Abstract: The temperature field and residual stress field in the Invar steel film of LNG ship tank was numerically simulated using finite element software MSC.Marc,and the calculation of fatigue life of the welded joint was carried out with the welding residual stress field coupled with the liquid sloshing pressure.The calculated results show that the longitudinal residual stress in the centerline on weld surface was about 298 MPa,and the peak value of longitudinal residual stress reached 328 MPa,higher than the yield strength (280 MPa) of the Invar steel at room temperature.Because of the existence of the welding residual stress,the fatigue life of Invar steel welded joint decreased from about 2.1×10⁶ to 1.7×10⁵.