The invention relates to a method and a device for measuring a post-combustion effect of a non-ideal explosive by an underwater explosion method. The method comprises the following step of: processing an impact wave signal and a gas bubble pulsation signal through underwater explosion by using an implementation device for enhancing the post-combustion effect of the non-ideal explosive under the condition that test conditions such as explosive amount, the size of the implementation device, gas pressure, underwater penetration of an explosion source, the position of a sensor relative to the explosion source and the like are identical so as to solve a specific energy value of the post-combustion effect of the explosive under the atmosphere of different gases; integrating a pressure time-interval curve of an impact wave to solve a specific impulse I and a specific impulse II respectively; and defining an indicator value phi which represents the post-combustion effect, wherein the definition of the phi is shown in the specification. When a selected integral form during impulse examination is the specific impulse I, a selected integral form during the impulse examination is the specificimpulse II, and tc in the formula means integral starting time, a decay time constant, namely required time when pressure is attenuated from a peak value pm to pm/e, of the pressure time-interval curve of a naked explosive is selected; when tend means integral end time, time when the pressure time-interval curve of the impact wave is attenuated to a position close to a base line is required to beselected; and p(t) which means the pressure of the impact wave is a function of time t.