Abstract: This paper presented an axle ultrasonic testing system of rail transport vehicle based on array overlapping imaging technology. The system aimed at defect prone parts on solid axle of rail transport vehicle and worked out a special array ultrasonic testing technology. Two sets of array ultrasonic testing scanning devices were designed and a multi-channel array ultrasonic data acquisition system with special testing software was developed. The multi-channel ultrasonic testing was able to detect the defect prone parts of axle without dead ends from the axle end and from the axle body, respectively, and it used several imaging methods to describe the defects of axles accurately, so the testing system improved consistency, repeatability and efficiency of current axle testing.