Abstract: The method of direct volume measurement via drainage is often applied in the process of measuring gas desorption in laboratory, but there are many problems such as too many people involved, large error in reading and complicated measurement process. The method of measuring gas desorption by drainage weighing is put forward, it can convert the mass of water discharged in the process of gas desorption into gas desorption volume through the relationship of mass, density and volume. The automatic design of the process of gas desorption measurement in laboratory is carried out based on LabVIEW on PC and PLC technology. The automatic measurement device is developed, it contains the industrial control system, desorption system and data processing system, which can automatically collect the real-time data of drainage mass, desorption environment temperature and pressure in the process of measurement, and completely avoid the possible error of manual reading as well as reduce the degree of personnel participation. The results show that the automatic measurement method is helpful to improve the accuracy of gas desorption measurement, and the error can be reduced by more than 10%.