Abstract: The theory of EMD （Empirical Mode Decomposition）‚as well as the correlation dimension （CD） and its characteristics‚was firstly discussed in this paper．Then‚according to the non-stationary feature and simple symptom monitoring of the vibration signals of a practical gearbox‚the methods of EMD and CD were pre-sented．These two methods are respectively applied to the analysis of nonlinear and non-stationary signals as well as the measurement of the nonlinearity and non-regularity of the observed time series for a system．An EMD＆CD method was finally presented for identifying the vibration signals of a gearbox．The results indicate that‚in various gear conditions‚the correlation dimensions of the intrinsic mode function related to the gear fault mode are obviously different with each other．This means that the EMD＆CD method can be used to extract the fault characteristics of a gear．

Key words: gear, fault diagnosis, empirical mode decomposition, correlation dimension