The manufacture methods and potential flaws of steel plate were analyzed. Automatic detection was conducted on steel plates using electromagnetic acoustic transducer technology. A research was carried out mainly in aspects including the electromagnetic acoustic transducer principle and sound wave，the selection and arrangement of wave shape of transducers， the reference blocked and its artificial defects desipn，setting of the detection gate，display of the test results and records etc. There search showed that a full-coveragen on-contact type scanning of the steel plate could be achieved by electromagnetic acoustic transducer. Hiph speed and hiph temperature test could be achieved. It could meet the test requirements for steel plates used for large-diameter，heavy-wall and high-pressure oil and gas line pipes. Hence，it provided reference to researching of by electromapnetic acoustic transducer for steel plates，and reference to formulating relevantst andards.