Disclosed is a method for preparing ammonia gas through a reaction between an ammonium salt and a silicate. An aqueous solution of the ammonium salt in the form of atomized droplets is contacted with a silicate at a high temperature for a reaction to generate ammonia gas and a solid substance. The silicate can be solid particles, and forms a bed. The generated ammonia gas is collected, the solid substance is extracted, part of the same solid substance is mixed with a fresh silicate solid particle, and the mixture continuously reacts with the atomized droplets of the aqueous solution of the ammonium salt.