The invention relates to the technical field of carbon black preparation through low-temperature desulfurization of waste tires, in particular to a method for preparing carbon black by desulfurizing the waste tires at low temperature through an ammonia method. The method includes the steps that the waste tires are cut into particles, then the particles make contact with ammonia gas in a circulating fluidized bed, in a normal-temperature environment, ammonia gas is introduced, bond energy of S-S bonds and S-C bonds in the waste tires is destroyed, and desulfurization difficulty and energy consumption are reduced; the steps of magnetic separation, grinding and magnetic separation are combined, then the particles and a desulfurizing agent are mixed by a certain ratio and are subjected to high-temperature pyrolysis in a pyrolysis treater; materials remaining from pyrolysis and the desulfurizing agent are mixed and treated ultrasonically, the sulfur content in the carbon black is reduced below 0.1%, and the quality of the carbon black is improved; ammonia gas treatment before entering the pyrolysis treater and desulfurizing agent treatment are combined, bond energy of the S-S bonds and S-C bonds in the waste tires is destroyed, the bond energy structure of C-C bonds is protected, the output of the carbon black is increased, and the quality of the carbon black is improved.