The mechanical equipment work is greatly influenced by gear wear failure.The acoustic emission detection technology is used to monitor the real-time state of gear running.Hilbert-Huang transformation（HHT） is used to analyze the collected data.Comparing the normal gear and the fault gear with their empirical mode decomposition and Hilbert spectrum

the frequency characteristics of the gear failure are obtained.So acoustic emission method is the effectively detect means for the gear wear failure and is great importance to the gear fault diagnosis.