The gear failure vibration diagnosiS in a gearbox is of great importance in manyfields.Through theoretical analysis and engineering application,two methods of gear vibration en-velope analysis technique are discussed in this paper.Zoom Hilbert transform en velope and zcomnarrow-band en velope are formed by applying zoom technique to Hilbert transform demodulationand narrow-band demodulation in order to increase the frequency resolution of demodulation spec-trum.