Abstract:In order to study the fatigue performance of cracked workpiece under ultrasonic loading, the tensile test of notched 20 steel was carried out by selfdeveloped ultrasonic uniaxial tensile test device. The specimen is designed that the both ends are square board, the middle is index profile, and single side opened a gap. The stress state of the notch specimen is theoretically analyzed, and the positive stress distribution formula of the notch groove section was obtained. By changing the notch groove depth t and curvature ρ of the specimen, it is obtained that the fatigue limit decreases with the deepening of the notch groove depth, reaching a minimum at a depth and then rising; the fatigue limit decreases with the decrease of the notch groove curvature, and reaches the minimum at a certain curvature, and then rises. The test shows that the fatigue limit is not only related to the stress concentration coefficient, but also to the depth of the grooves, stress gradient and other parameters,and the present work shows it is necessary to further study in this research field.