The invention discloses a method for measuring the fracture toughness J of each micro area of a heat affected zone of a welded joint, which is applicable to measurement on fracture toughness of various welded joints. According to the method, by forming a V-shaped groove in a coarse grain zone or a fine grain zone in the welded heat affected zone on a three-point bending test sample, the direction of crack development is effectively controlled to ensure the crack development in the coarse grain zone or the fine grain zone in the heat affected zone, and thus the fracture toughness of the different micro areas in the heat affected zone of the welded joint can be measured. The method is simple, is low in cost, ensures real and reliable measurement results, and has great significance for evaluating the mechanical property of each micro area of the welding joint, confirming a weak section of the welded joint and studying the fracture toughness of the heat affected zone of the welded joint.