The invention relates to a method and device for detecting fault electric arc based on time-frequency comprehensive analysis. The method comprises the following steps of: (1) resetting power-on; (2) initializing a system; (3) initializing parameters, and assigning values for the parameter; (4) opening timed disconnection and starting A/D (Analog to Digital) conversion; and (5) acquiring output voltage signals and the like of a signal conditioning circuit and an amplitude detecting circuit in real time with a microprocessor by taking Tsample time as a sampling interval. The device comprises a current mutual inductor, a voltage following circuit, an amplitude detecting circuit, a power supply module, a signal conditioning circuit, a microprocessor, a tripping driving circuit, a tripping action mechanism, a resetting circuit, a testing circuit and an LED (Light-Emitting Circuit) indicating circuit. Compared with the prior art, the method and device have the advantages of low computing complexity, high security, low cost and the like.