The invention relates to a high-pressure grouting process of a water-rich weathering fracture rock formation below a thick unconsolidated formation for a coal mine. The process at least comprises the following steps of A) pipe fixing grouting, B) secondary drilling, C) grouting core pipe mounting and D) high-pressure grouting. Therefore, a thin grouting core pipe is tripped in a grouting hole, clearances are formed among the grouting core pipe, a secondary drilled hole and an orifice pipe, a pipe fixing and grouting stopping device is arranged on the front segment of the grouting core pipe, the pipe fixing and grouting stopping device is filled with pipe fixing materials, a thick pipe fixing layer can be formed, the pipe fixing materials cannot enter the stratum below the grouting stopping device, and it is guaranteed that the section of a grouted layer is fresh and is not polluted by pipe fixing liquid. The physical, chemical and mechanical property of the formed pipe fixing layer is stable, the continuity of the pipe fixing layer in the clearances is good, few defects exist, large grouting pressure can be borne, construction efficiency is greatly improved, grouting efficiency is high, grouting cost is low, the grouting effect is good, and the process can adapt to fast water plugging of water burst accidents.