Abstract:According to the problems existing in envelope feature extracting methods that were based on Wavelet Packet Transform (WPT) or Empirical Mode Decomposition (EMD), this paper adopts signal decomposition method of EMD and WPT combination in feature extracting. This decomposition method can not only provide high resolution, but also avoid error messages caused by false Intrinsic Mode Functions (IMF) components. After the combination of envelope features are extracted using EMD and WPT method, the most effective characteristics of defected signals will be selected and classified using the data feature selecting method based on Principal Components Analysis (PCA). Based on the above features extracting and selection methods, this paper uses mixed programming of Labview and Matlab to develop a diagnosis system for S700K-C electrical switch machine, and the diagnostic testing experiment in the end proves that this diagnosis system can extract defected signals accurately and rapidly.