The invention discloses a technology of desulfurizing an ammonia-ammonium sulfate wet flue gas and inducing crystallization to recover the ammonium sulfate. The technology comprises the following steps: ammonium sulfate solution is used as an absorbent to contact with the flue gas; sulfate dioxide in the flue gas is dissolved and absorbed; the absorbent absorbing the sulfate dioxide reacts with ammonia to generate ammonium sulfite; after the ammonium sulfate is generated by oxygenization, crystallization is induced; ammonium sulfate crystals are recovered; and the ammonia is not used for desulfurizating the absorbent, which enhances the using efficiency of the ammonia and reduces the escaping of the ammonia. In addition, in the process of the crystallization of the ammonium sulfate, the method for inducing crystallization is used for reducing the evaporation using amount in the traditional technology and accelerating the crystallization speed, which not only saves the operation cost and reduces the energy consumption, but also enhances the stability and reliability of the system.