Abstract: In order to advance the accuracy and the reliability of direct determination gas content, researchers tested desorption of the two coal samples in laboratory which were from No.11 mining area of Cuimiao and No.32 mining area of Peiguo.Desorption law is statistically analyzed by related mathematical software and then the two coal sample desorption laws are drawn out.It is found that the logarithmic function is better than other leakage calculation formulas by comparison research on Barrer,Sunchongxu and Wangyouan.Logarithmic function and some suggestion are proposed to use in the loss quantity calculation of direct determination gas content in engineering.