The invention discloses a hydrolysis reactor automatic switching control method for an ammonia production system, which comprises the following steps: preheating a second reactor, and controlling thepressure of the second reactor to ensure that the pressure of the second reactor is stable to finish preheating preparation before switching of the second reactor; continuously adjusting the temperature of the second reactor to a first preset temperature value; controlling the urea flow according to a second preset flow value matched with the minimum ammonia demand; reducing switching fluctuations, meanwhile, when the temperature, the pressure and the urea flow of the second reactor are respectively in a preset deviation range, controlling the second reactor and the first reactor to increase and decrease the load in a preset mode until the urea flow of the first reactor meets the requirement, and finishing switching. The switching process is small in switching fluctuation, the pressure ofthe ammonia gas main pipe is effectively controlled to be stable, the ammonia gas yield meets the boiler requirement, and NOX overdischarge and ammonia gas leakage exceeding the standard of a boiler system are prevented; the production condition is continuous and stable, the workload of operators is reduced, the production efficiency is improved, and safe production is ensured.