Abstract: The gas content and desorption rate of coal reservoir have important influence on the high and stable production of CBM well. In order to quantitatively evaluate the desorption rate of coal samples, and to reduce the test time of desorption gas content, this paper builds a quantitative relationship between absorption rate and desorption time based on desorption experiment data of coal samples from Jiergalangtu Sag of Erlian Basin. And the quantitative relationship between desorption time and cumulative desorption gas content is established, based on this, a new desorption gas testing methods is proposed also. The results show that the desorption rate of coal sample decreases with the increase of desorption time. The larger the initial desorption rate value, the smaller the desorption rate, the larger the desorption rate of coal formation. The desorption curve of coal sample can be quantitatively characterized by formula.