Abstract: In this paper, anthracite was pretreated with NaOH solutions with concentrations of 0.01, 0.1, 0.3 mol/L. And the effect of NaOH pretreatment on the conversion of anthracite to biomethane was studied through testing the biomethane production of residual coal, filtrate and mixture obtained by pretreatment of different concentrations of NaOH. The results show that the high concentration of NaOH pretreatment can significantly increase the gas production of solid residual coal; methane was detected after anaerobic degradation of the filtrate, indicating that NaOH acts on the coal structure to dissolve small molecules of organic matter; the sum of gas production of coal and filtrate is significant more than the gas production under mixed conditions, therefore, in practical engineering application, the liquid produced after coal seam pretreatment can be extracted first and then injected with microorganism to improve gas production.