Abstract: The gas content test period was so long with the combination methods of underground test and laboratory test in China.An underground portable rapid d eterminator for gas content was made based on coalbed gas desorption velcity method, and it could obtain results of gas content in 30 minutes in situ underground, so the test period was shortened greatly.The key technologies of the underground portable rapid determinator was proposed.Research results showed that coalbed gas de sorption velocity measurement should use multi-range sensor combination and intelligent select the adaptive range, the characteristic parameter of gas desorption velo city V1 should be determined by regression analysis using the first three minutes data of gas desorption velocity, and the linear regression constants Aand B of W-_V1 s hould be determined by both field test method for V1 and vacuum degassing method for gas content W.The field application shows that the average deviation of the det erminator is 4.36% comparing with laboratory test method.So the determinator can meet the needs of gas content determining in high gassy mines and coal and gas out burst mines.