The invention relates to a dense colloid used in fire hazard treatment in coal layer, wherein it is formed by water, skeleton, and densifier; the skeleton is one of cola ash, loess, sand or stone powder; the densifier is one or several of carboxymethyl cellulose, cellulose ethyl ether, carboxymethyl hydroxyethyl cellulose, cellulose methyl, carboxyethyl cellulose, hydroxypropyl cellulose methyl, butyl cellulose, glycol cellulose, and hydroxypropyl cellulose; when using, mixing the water, densifier, and skeleton to be poured into fire area. The inventive colloid has strong water kept ability, and better adhesive with the coal, to effectively pack high-temperature coal, and improve the fire extinction effect; and the water and skeleton are not easily separated, to prolong the cooperation between them, reduce the evaporate speed of said product in high temperature to avoid explode water gas.