The utility model discloses a flue gas SCR denitration urea seeding system ammonia system of hydrolysising, including reaction system, urea solution feed system, steam supply system, the empty hybrid system of ammonia, catalyst feed system, blowback system and blowdown and safety coefficient, it dissolves the inlet port to be equipped with catalyst inlet port and urea on the reaction system, catalyst feed system provides the catalyst through catalyst inlet port back reaction system, the urea solution feed system provides urea solution through dissolving the urea solution pipeline back reaction system that the inlet port is connected with urea, the ammonia of reaction system export gets into the empty hybrid system of ammonia through the ammonia pipeline and dilutes, set up drain and pressure release mouth on the reaction system, be connected with blowdown and safety coefficient through waste liquid discharge tube and exhaust emission pipeline. The utility model discloses a system has urea, and to hydrolysis fast, the ureal consumption of speed short with the hydrolysis reaction time less, realizes the automatic advantage.