In order to diagnosis the fault of worm and gear reducer caused by worm gear tooth profile changing
a kind of acquisition system for collecting the vibration signal of reducer is designed.For extracting the characteristic frequency from fault vibration signals
the method of combining the empirical mode decomposition(EMD)and Hilbert transform is proposed.The vibration test results of normal and fault worms show that
the method got the same results as using JD45+ gear measuring instrument.The effectiveness of the method for diagnosing the worm gear tooth profile change fault of worm reducer is verified.