The filtering property of empirical mode decomposition is analyzed in the paper. Aimed at the low signal/noise ratio and non stationary feature of vibration signal of cyclic machine, EMD is introduced to the noise reduction of vibration signal and the useful signal is given prominence efficiently, which offers the more efficient foundation to monitor on line and fault diagnosis of cyclic machine. By the simulation and application, it shows that EMD is very useful in reducing noise and provides new means of vibration signal analyzing.