Abstract: The desorption time of coal bed gas is an important parameter in the production of coal bed gas. It directly affects the gas production rate of coal bed gas wells and determines if the gas production peak comes earlyor late. By analysis on the factors which affect desorption time, the authors considered that coal rank, ash content, temperature, microlithotypes, the developed degree of cleat and the grain size of coal samples are the most important factors to affect desorption time. The desorption time of major coal bed gas basins in China is generally 0.17～27.42 day. The sensibility of desorption time to gas production shows that the desorption time of coal bed gas in China has little influence over the monowell production of coal bed gas.