NOVELTY - A coated sustained release agent is prepared by dissolving polyvinyl alcohol into heated industrial purified water in reaction kettle, adding hydrochloric acid solution, adding formaldehyde solution with water content of 4-7%, maintaining temperature at 80-85 degrees C, stirring, adding ammonia solution, adding urea with water content of 2-4%, reacting for 20-30 minutes, adding pure acrylic emulsion, stirring, reducing temperature to 40-50 degrees C, adding film-forming agent and polyoxyethylene (10) nonylphenyl ether, adding bentonite, and stirring for 20-30 minutes.    USE - Preparation of coated sustained release agent for fertilizer (claimed).    ADVANTAGE - The sustained release agent forms films continuously; has better effect for forming films by using the film-forming agent and has excellent sustained-release performance; can be degraded easily; and does not pollute the soil.    DETAILED DESCRIPTION - Preparation of coated sustained release agent comprises:    (A) adding industrial purified water to reaction kettle, heating to 94-98 degrees C, adding polyvinyl alcohol with water content of 9-11%, and stirring for 1.5-2 hours until polyvinyl alcohol is dissolved to obtain a polyvinyl alcohol solution, reducing temperature to 80-85 degrees C, and adding hydrochloric acid solution into reaction kettle to adjust pH to 2-3;    (B) adding 37% of formaldehyde solution with water content of 4-7% to reaction kettle, maintaining temperature at 80-85 degrees C, stirring for 30-35 minutes, adding ammonia solution to adjust pH to 7-8, adding urea with water content of 2-4%, and reacting for 20-30 minutes so that urea react with formaldehyde; and    (C) adding pure acrylic emulsion (1.5-2 times the amount of polyvinyl alcohol solution) into reaction kettle, stirring for 20-30 minutes, reducing temperature to 40-50 degrees C, adding film-forming agent (0.4-0.6% of total amount of polyvinyl alcohol solution and pure acrylic emulsion) and polyoxyethylene (10) nonylphenyl ether (0.05-0.1% of total amount of polyvinyl alcohol solution and pure acrylic emulsion), adding bentonite (8-12% of total amount of polyvinyl alcohol solution and pure acrylic emulsion), and stirring for 20-30 minutes.