Abstract: For ultrasonic detection of the steel plate edge,traditional practice is to mechanically fix the detection system onto the main beam of the gantry support.In this case,the mechanical conjunction area is damaged due to the irregular edge profile of the plate,and thus untrue detection data would be produced.Elaborated in the article is a newly-developed automatic UT system for edge inspection of the steel plate,involving such aspects as the structural features,the process flow,and the operating principle and characteristics.Based on the operation effectiveness of the said UT system,it is concluded that thanks to the closed-loop control of the detection operation by a pneumatic-electrical control system,the UT system is capable of automatic edge detection of the steel plate,and that the design is reasonable,which results in true and reliable detection data,and flexible adjustment and control of the system as well.