Abstract: In this paper，based on the desorption performance of No.3 and No.7 outburst coal seams in Qinan Coal Mine，the physical simulation direct method was used to study the influence of sampling timeonthe calculation accuracy of lost gas in direct measurement method of gas content，and the lost gas content was calculated by adopting Barrer formula based on the desorption data．The results show that the error of the calculated and actual lost gas contents is direct proportion to the logarithm of reading time interval，and will decrease when the initial linear measuring points of gas desorption decreases．Thus，it is suggested to chose 4~10 initial linear measuring points of gas desorption．When controlling the ratio of the difference value of actual and calculated lost gas content and the measuring results of direct method into 10%，the effective sampling control time will show a linear relationship with the gas pressure，and with the increase of gas pressure，the sampling control time will be decreased．

Key words: gas content；direct method；Barrer formula；effective sampling time