The invention relates to a switch failure diagnosis method based on radiation electric field characteristic energy extraction. The method is characterized by comprising the following steps: (1) adopting a wavelet packet analysis method for qualitatively analyzing and quantitatively calculating a typical transient radiation electric field pulse generated by a switching action under the normal working state, thereby confirming a characteristic frequency band of an electric field pulse signal, and then solving the characteristic frequency band energy, thereby acquiring a characteristic frequencyband energy value of a switching transient electric field pulse under the normal state and using as a reference energy value; and (2) measuring the electric field pulse signal generated after the action of the switch at each time, calculating the characteristic frequency band energy, comparing with the reference energy value acquired in the step (1), confirming as insulation fault of the switch ifthe two has a larger difference, otherwise, confirming as no insulation fault of the switch. According to the invention, the two can be directly distinguished according to the magnitude of the energyvalue, so that the effect of accurately diagnosing the failure of the switch can be achieved.