Abstract: The welding quality of the propellant tank has a significant effect to the life and the reliability of satellites. To study the influence of the residual welding stress on the fatigue crack on the tank, the welding residual stress is first calculated with a spherical and a planer model, respectively. The stress intensity factors of three kinds are introduced to investigate the relations between the shape factors of the crack on the most vulnerable area with the highest stress intensity. The values and the variation trend of the crack’s stress intensity factors against the crack morphology are obtained. It’s shown that among the three SIFs, K_I plays a most important role; K_II is subjected more to the crack angle; the value of K_I and K_II both reaches its minimum at the center of the crack; and the value of K_III basically increases with the normalized front of the crack.