The invention discloses an efficient sewage ammonia nitrogen removal agent which consists of the following components in parts by weight: 30-50 parts of magnesium salt, 20-45 parts of phosphate, 10-15parts of ferric sulfate, 10-20 parts of calcium carbonate, 5-10 parts of modified bentonite, 10-20 parts of modified coal ash, 5-15 parts of modified zeolite, 2-10 parts of an attapulgite compound adsorbent, 20-30 parts of sodium hypochlorite and 5-12 parts of a coagulant aid. The efficient sewage ammonia nitrogen removal agent has the beneficial effects that metallic salts, phosphate and ammonium ions form precipitate in water, effective adsorption and ion exchange of ammonia nitrogen in the water can be carried out through the modified bentonite, the modified coal ash, the modified zeoliteand the attapulgite compound adsorbent, ammonia in the water can be converted into nitrogen which is removed later through the sodium hypochlorite, the pH value of sewage can be adjusted by the calcium carbonate, the flocculation effect of the precipitate can be improved by the coagulant aid, precipitate sedimentation and separation can be promoted, and the agent is applicable to wide pH value ranges, has a good treatment effect on low-concentration ammonia nitrogen wwaste3water, and is environmental-friendly.