A device for testing the rate of inflammable gas given off when matter meets water is characterized in that a constant voltage separating funnel with a side pipe is communicated with a conical beaker by a three way pipe; the conical beaker is arranged in a thermostatic water bath circulator which is internally provided with water bath for heating and cooling; the side pipe of the constant voltageseparating funnel and the outlet of the bottom thereof are respectively provided with a switch; the outlet at the side of the three way pipe is communicated with the air inlet of a flow meter; the air outlet of the flow meter is communicated with a surge flask; the input end of a monitor is connected with the output end of the flow meter. The device can be used for judging fatalness when the matter meets wet, has the real time supervisor control function, does not need manual time-keeping, weighting and calculation; after the testing is over, the starting time of the testing is input, and then the real time monitoring data can be led out, thus avoiding the problem that the manual weighting can not exactly measure the rate of inflammable gas given off when the matter meets water, meanwhile, saving the precious manpower and time and greatly improving work efficiency.