The invention provides a density conditioning agent for a high polymer and a preparation method of the density conditioning agent. The preparation method comprises the following steps of: modifying the coal ash which is taken as a raw material by an alkaline modifier and an acid modifier sequentially, and activating by a coupling reagent. The prepared density conditioning agent for high polymer is used for the high polymer products, and has the advantages of being high in applicability and high in compression strength, improving the flowability, the abrasive resistance, the carving resistance, the corrosion resistance, the pollution resistance and the weather fastness, being good in gloss controllability and flexibility, improving the high temperature-resistant fireproof performance, having the functions of heat preservation and heat insulation, being good in rubbing property, improving the work efficiency, being low in cost and the like; and the oil value can be reduced, the processability can be improved, the loading level can be increased, and the production cost of the high polymer product producing enterprises can be obviously reduced, so that the density conditioning agent is wide in application prospect in the industries, i.e. the plastics, the rubber, the asphalt and the like.