The invention provides a reaction device for preparing ammonia by urea hydrolysis. The reaction device for preparing ammonia by urea hydrolysis comprises a reactor, a heating component and a urea solution circulating pipeline; the reactor is used for providing a reaction place for a urea solution to be hydrolyzed; the heating component is provided with a heating part which is positioned in the reactor and used for heating the urea solution, and the contact interface between the heating part and the urea solution is provided with a corrugated curved surface, wherein the corrugated curved surface comprises a plurality of convex parts arranged at intervals and a plurality of concave parts arranged at intervals, and the convex parts and the concave parts are sequentially connected to form thesmooth curved surface; and one end of the urea solution circulating pipeline is connected with a urea solution circulating outlet of the reactor, and the other end of the urea solution circulating pipeline is connected with a urea solution circulating inlet of the reactor. Scaling of impurities in the urea solution on the surface of the heating component is reduced while heat exchange efficiency is increased, and cleaning and maintenance cost is reduced.