NOVELTY - Method for producing highly pure hydantoin, involves producing hydroxyacetonitrile aqueous solution by reacting hydrocyanic acid as raw material with formaldehyde absorbent material, preparing aqueous solution of obtained compound and ammonium carbonate, obtaining concentrated hydantoic acid aqueous solution, cooling, crystallizing, isolating crude hydantoin, carbon dioxide, ammonia and water, carrying out heat-treatment of crude hydantoin using purification agent with activated carbon, dissolving in hot water, obtaining hot solution of pure hydantoin, cooling, crystallizing, separating and drying.    USE - Method for producing highly pure hydantoin (claimed).    ADVANTAGE - The method effectively avoids decomposition and polymerization of hydroxyacetonitrile, inhibits generation of harmful impurities, realizes high yield, and allows the purity of the obtained product to be very high. The method reduces the device investment, and guarantees the operation safety of the whole process. The hot water dissolving, heat treatment and hot filtration are adopted in the purifying process, so consumed energy is saved. The whole method is a thoroughly environmentally-friendly and clean. The method has lower requirements on raw materials, can fully and comprehensively utilize resources, and plays an active role in natural environment protection.    DETAILED DESCRIPTION - The method for producing highly pure hydantoin, involves producing hydroxyacetonitrile by reacting hydrocyanic acid as raw material with formaldehyde absorbent material, preparing aqueous solution of ammonium carbonate and obtained compound at room temperature and heating with aqueous ammonia in a reaction system, carrying out pressure synthesis of hydantoic acid, continuing to release pressure, evaporating and concentrating to release carbon dioxide and ammonia, obtaining concentrated hydantoic acid aqueous solution, cooling, crystallizing, isolating crude hydantoin, carbon dioxide, ammonia, and water, and recycling ammonia containing water in recycling system, carrying out acid recovery using crude crystal liquor loop solution, carrying-out heat-treatment of crude hydantoin using purification agent with activated carbon , dissolving in hot water, implementing thermal filtration, obtaining hot solution of pure hydantoin, cooling, crystallizing, separating, drying to obtain high purity hydantoin, and recovering main liquor used as solvent of hot water heating cycles.