Abstract: This paper deals with the welded joint fatigue of a cylindrical pressure container simulated on a cross-shaped weld test plate with biaxial tension. The investigation was based on the J integral and the principle of strain energy. The experimental results show that the expression da/dN=C(ΔJ)^m coincides with the law of fatigue crack extension of a welded joint under the action of alternating stresses cavsed by a biaxial tension and is applicable to estimate the fatigue life of a pressure container.