Abstract: The traditional method of drainage gas collecting is affected by human and environment, which is easy to produce errors and is not convenient for automation. In this study, the gas volume of a foaming agent can be calculated by measuring the gas pressure change of the foaming agent in a fixed volume closed container. At the same time, the starting temperature, jumping temperature, ending temperature, maximum gas volume and other parameters of foaming agent can be obtained by measuring the gas pressure in a fixed volume closed container, so as to monitor the whole foaming process of the foaming agent. The gas pressure of a foaming agent measured in a fixed volume closed container can be converted into the gas volume of foaming agent measured by the drainage gas collecting method, by establishing the functional relationship between the gas pressure in a fixed volume closed container and the gas volume of a foaming agent. The gas volume curve of a foaming agent measured by the drainage gas collecting method can also be transformed (change with temperature) to the pressure curve in a fixed volume closed container (change with temperature). In this paper, Azodicarbonamide (ADC) was selected to verify the feasibility of the formula.