The invention discloses a method for detecting the state of a gap of a DC switch. The method comprises the following steps of step A) performing isolated collection on a real-time action current I of the DC switch, and collecting a real-time working
voltage U of the switch; step B) according to the real-time action current I and the real-time working
voltage U, performing calculation so as to obtain a real-time power P=U*I of the DC switch; step C) according to the real-time power P of the DC switch and a speed V of a switch
machine, performing calculation to obtain a resistance F=P / V of switch movement, so as to draw a resistance fitting curve of the switch movement; step D) analyzing the resistance fitting curve of the switch movement, and judging whether the resistance fitting curve is a normal movement state of the gap of the switch
machine or not; and step E) according to the movement state of the gap of the switch
machine judged in the step D), outputting a switching value
signal of the corresponding gap state. According to the method disclosed by the invention, mounting
video equipment, providing an additional
electricity supply circuit and providing a high
wideband are not needed, and the method is simple in construction, safe in monitoring, low in cost and accurate in testing results.