Abstract: Electromagnetic acoustic transducer technology (EMAT) is a branch of ultrasonic nondestructive testing. This technology utilizes interaction between electromagnetic fields to generate ultrasonic waves. The technique directly generates waves on the surface of the material. Therefore, no couplant is needed. In service thickness measurement of pressure piping at high temperature is a very hot topic in the field of NDT. Measure and monitor the corrosion of critical piping condition without stopping its usage provides enormous benefit to the safety of plants as wells cost savings. Conventional ultrasonic testing with high temperature probes and couplant is one option. However, the disadvantage is that the evaporation of the coupling puts very stringent requirements on the operator to get good measurement data. In addition, the high temperature couplant is also very costly to be used in a large amount. In this paper, the basic principle of EMAT technology, the equipment and sensors for thickness measurement, unique features of operation were all introdued. And also the laboratory and field test results and analysis were supplied. At last, we can get the condusion that EMAT technology fills in the need of high temperature thickness measurement because couplant is not needed for the inspection.