Gas content measurement is a common technique in the prevention of coalmine gas disasters. During the measurement, the gas desorption amount of field coal samples needs to be obtained by an instrument working under the principle of gas collection by water displacement (GCWD). The instrument is poorly automated, and susceptible to the influence of subjective factors. To overcome these defects, this paper designs an automatic detector of gas desorption, aiming to realize automated detection. Firstly, the authors analyzed the gas desorption detection process, and clarified the contents and features of the information to be collected. On this basis, the hardware and software systems of the multi-data automatic detector were developed based on digital circuit design and multi-sensor detection. To further improve the measuring accuracy of gas desorption, the multi-range multi-stage mode was introduced to the automatic detector. Application results show that the proposed detector can automatedly collect and store gas desorption amount, ambient pressure, and temperature, greatly improve the degree of automation, and minimize the influence of subjective factors. The popularization of this detector will make gas desorption measurement more efficient and effective, laying a solid basis for the prevention of coalmine gas disasters.