Abstract: In order to recognize changes in the running state of vehicle transmission,methods of recognition of break changes by wavelet transformation and recognition of gradual changes by middle threshold de-noising from state data monitoring in time domain are described,and an improved procedure of computing the threshold is described.From the angles of the energy spectrum and distribution of feature frequency,ways of analysis on the tendency of signal in frequency domain are presented,and a method of solving frequency mixing is discussed.The result shows that the information indicating the changes of the running state included in data monitoring can be extracted in the time domain and frequency domain by wavelet transformation.