Abstract: Elaborated in the paper isan on-line 210 channel，100% coverage ultrasonic detection system for steel plate defects，involving such aspects as the layout，themechanical structure，system configuration of the electric control equipment，configuration of the drive system，arrangement of the electric facilities，process principle of the equipment，the technical data and functions，etc.With this detection system，for detection of both head and tail of the steel plate，the operation mode is getting the material fixed，and the probe moved.For plate edge detection，adjustment is made along the width direction of the plate according to the width of specific plate.During the operation，the system can perform tracking-floating detection of the plate edge along with the profile of the plate. Thus，full thickness coverage detection is realized with the system，havingmet the requirements for steel plate 100% UT inspection and the working conditions.