Pulsed Energy is a kind of electrical signal, which is not varying in sinusoidal waveform and accompanying mutation. It is important to study to the feature information of pulsed energy. The paper proposes a new method to extract some mutations and decision rules based on S time-frequency analysis, then find the feature components of Electrical Discharge Machining based on the S spectrum. The results show that it is the effective method to study the mutation features of pulsed energy.