Abstract: To verify the effect of microbes on gas generation of coal beds, microbial simulation experiments have been made on different coal ranks. The result shows that microbes in coals can produce gas by themselves under laboratory conditions. With comparison of experiments under different temperatures, the gas production under 35℃ is greater than that under 15℃, indicating that it is more suitable for microbes to produce gas under 35℃. According to quantitative experiments, it is shown that the gas production is improved by adding exogenous nutrients or exogenous bacteria. Moreover, the production enhancement ratio can reach 115% by adding exogenous bacterial species and 144% by adding nutrients.