The invention relates to a thick-wall adapter tube weld joint ultrasonic testing device which is mainly applied to ultrasonic testing of weld joints of thick-wall adapter tubes (the inner diameters of adapter tubes are more than 150mm, and the wall thickness is more than 20mm) of pressure-bearing equipment in a large ground test device in an aerospace system. The adopted scanning device can do axial and peripheral movement, the structure is simple and practical, the traditional ultrasonic A scanning manual operation is replaced by motor drive, the structure is small and flexible, and the detection efficiency and the detection accuracy are improved. The zigzag ultrasonic A scanning perpendicular the weld joint is changed into rectangular ultrasonic A scanning parallel to the weld joint, a mechanical motion mode is simplified, and automatic scanning is conveniently realized. The device is controlled by a control panel, so that a detector can perform ultrasonic testing in the distance, harm caused by field harmful volatile matters and other unsafe factor is avoided, and the labor intensity is alleviated. The device also can be used for detection of other planes or large-diameter pipelines.