The invention relates to a method for large diameter borehole extracting and high-pressure grouting hole sealing, which is characterized in that the method comprises the following steps: at the coal seam top and in the floor roadway rock surface, an across-seam hole drilling and sealing section are constructed in the coal seam; a hole sealing pipe is positioned into the hole sealing stage; a grouting cavity is reserved between the hole sealing pipe and the hole wall of a borehole; a grouting pipe and a return pipe are respectively arranged in the two positions corresponding to the grouting cavity; the output pipe of a high pressure grouting pump communicates with the grouting pipe; grouting material is infused into the grouting cavity by the high pressure grouting pump through the grouting pipe, until the grouting material overflows out of the return pipe; the hole sealing section is formed through maintenance; across-seam hole drilling is constructed in the inner cavity of the hole sealing pipe. The method has the advantages that the hole sealing effect is good, the effective gas extraction time is long, and the construction method is simple.