The invention belongs to the technical field of environment protection, and relates to a device and a process for temperature difference crystallizing ammonia process desulfurization, which is especially suitable for the ammonia process modification and newly-built desulfurization of the original calcium process desulfurization device. The device comprises a desulfurization tower, a densifying device, a gas-liquid heat exchanger, a circulating pump, a concentration circulating pump, a magma pump, a concentration crystallization tank and a drying system, wherein the desulfurization tower, the circulating pump, the magma pump and the drying system adopt the devices in the original calcium process desulfurization; the lower part of the densifying device is provided with a gas distributor, andthe upper part thereof is provided with spray heads which are arranged in 2-3 layers; spray heads in the desulfurization tower are arranged in 2-4 layers, a liquid supplementation pipe is connected with the spray heads at the lowest layer in the desulfurization tower; the concentration crystallization tank is a tank with a conical bottom part; and the upper part of the concentration crystallization tank is provided with a pipeline to be connected with the bottom of the densifying device, the middle of the concentration crystallization tank is provided with a pipeline to be connected with theconcentration circulating pump, and the bottom is provided with a pipeline to be connected with the magma pump. The invention can farthest utilize the original devices on the premise of guaranteeing the normal desulfurization efficiency, thereby saving the investment, reducing the energy consumption and eliminating the secondary pollution.