In order to predict the fatigue life of the welded frame of 3B0 locomotive exported to Burma, the stress state of welded frame under different fatigue loading cases by FEM was analyzed, and then the fatigue stress ranges of main welds in box girders were determined. Based on IIW standard and fatigue test data in relevant literature, several S-N curve equations of welded joints for assessing the fatigue strength of welded frame was obtained, then the life cycles of some key welds were calculated by using both global nominal stress method and local notch stress method. The result indicated that the fatigue life cycles of all welds were greater than 2 million, which met the requirements of welded joint design standard for rail vehicle; As the T joint in frame’s side beam under vertical dynamic loads had low life cycles, it should reduce the local stress concentration by weld grinding. Normal stress method generally was partial to be conservative, so it had more advantages by using notch stress method for fatigue life prediction of welded structure from the perspective of structural light weight and local optimization.