The invention belongs to the technical field of super-gravity crystallization, and provides a method for crystallizing monoammonium phosphate through a super-gravity direct heat exchange method and a device in order to solve the problems that in existing monoammonium phosphate crystallization, the size of a crystallizer is large due to the fact that the heat exchange wall face of the crystallizer is deposited and the heat exchange efficiency is low, and products are nonuniform in particle size distribution and difficult to separate due to the fact that the cooling time is long and the temperature and concentration gradients are large.The method comprises the steps that monoammonium phosphate slurry to be cooled and inert medium gas are continuously introduced into a super-gravity device, direct heat exchange crystallization is performed by adjusting the liquid flow, the rotating speed of the super-gravity device and the reaction temperature, crystal nucleuses obtained through reacting continuously complete heat exchange and the crystal growth process in a constant-temperature crystal growing device, and crystals are prepared at a discharge port of the crystal growing device.According to the method, the process equipment is small in size and convenient to arrange in a plant; compared with a traditional technique, the heat exchange area is increased by 50%, the heat transfer efficiency is improved by 25%, the filtering time is shortened by one quarter, the uniform degree of the products is improved, and energy consumption is reduced by 25%.