Abstract: In view of the low efficiency of wheel detecting device, an online wheel detection system based on electromagnetic acoustic technology has been investigated. This device combines the advantages of surface wave and electromagnetic acoustic technology, by setting six detecting devices in the rail track to inspect the whole wheel surface. By adopting orthogonal test method to optimize electromagnetic acoustic transducers, the systems detecting ability is improved. Surface wave is excited by high power transmitting circuits and received by low noise receiving circuits. Control of the device and acquisition and transmission signal are accomplished by FPGA. The software on computer is developed to process data and display results. Experiments show that the system could detect flaws on the wheel surface efficiently, which indicates the device has advantages of independent of couplant and high testing efficiency.