Abstract: In order to improve the gas drainage effect in coal seam, the key is to improve the sealing method of boreholes. For the borehole extraction along this coal seam, a new type of colloidal material with coal ash as the base material and cellulose thickener, resin, expansion agent, water retention agent, superfine cement and surfactant as accessories was developed, the viscosity, expansibility and sealing properties of the new colloidal materials were determined by experiments. In the coal mine site, every 4 near-horizontal boreholes in this coal seam were taken as one group to conduct a controlled experiment to compare the sealing effect of conventional cement mortar, polyurethane and new colloidal materials. The results show that the concentration of gas extraction (methane volume fraction) was below 10% after 30 days of the traditional sealing method, and the new colloid material can reach more than 40%. The concentration and flow rate of gas extraction are significantly higher with new colloid material sealing technology than in conventional sealing method. Moreover, the secondary grouting can be carried out after the deformation of the borehole, so as to block the newly-formed cracks generated by the borehole in real time, which is conducive to the efficient and continuous extraction of coal mine gas.