Abstract: For problem that it was difficult to achieve evaluation grade A due to a long time reverse gap in DC power port voltage of intrinsically safe sensor in positive surge immunity test, taking a typical mine-used intrinsically safe methane sensor as research object, simulation models of combination wave generator, coupling-decoupling network and equivalent circuit of the sensor were established in ADS simulation software as well as a simulation circuit of surge immunity test at DC power supply port of the sensor. Transient process of the test was analyzed according to transient simulation waveform. The research results show that the reverse gap in DC power port voltage of the sensor is the secondary effect caused by surge protection component, and simulation waveforms are the same as the actual ones, which verify rationality of the transient analysis method.