In the paper, we developed a non-intrusive on line detection device based on wireless network electromagnetic valve for the on-line detection problem of electromagnetic valve in hydraulic system. The device used the vibration detection of non-intrusive and magnetic detection method. When sensitive electromagnetic coil is energized, the coil produced the changed signal. Besides, with the movement of electromagnetic valve’s core, it produced the vibration signal and transmitted the signal to the surface of valve body. For these two kinds of signal, then we used frequency bands energy based on wavelet decomposition. We could distinct the normal state and fault state of electromagnetic valve. So we could determine the work state and fault mode of the electromagnetic valve under test. And the designed detection device could achieve non-intrusive valve on-line detection of the valve, which was verified by experiments.