Abstract: Aiming at the crack position and area in the electron beam weld of the workpiece, ultrasonic testing method of special wave mode conversion wedge combined with longitudinal wave straight probe was proposed. According to the crack location and detection area, the comparison sample was made. There were EDM grooves with different depths on the comparison sample to simulate cracks with different depths. A special wave mode conversion wedge was designed and manufactured according to the position of annular electron beam weld, surrounding structure, transverse wave beam angle, sound beam center position, longitudinal wave straight probe, weld width and weld thickness. Through the test, the EDM grooves with different depths on the comparison sample could be detected. This method could be used to detect the electron beam weld crack of the workpiece.