The invention discloses an ultrahigh-flowability AS granule and a preparation method thereof, and provides a preparation method for the AS granule, which is easy to process and has ultrahigh flowability, in the situation of low influence on the property of ABS resin. The invention belongs to the field of plastic chemical engineering production. The material is prepared from, by weight, 55 parts ofstyrene, 19 parts of acrylonitrile, 54.5 parts of a circulating monomer, 0-20 parts of a chain transfer agent, and 0-2 parts of a chain initiator. Compared with the prior art, the preparation methodhas reasonable processes; and the product is low in viscosity and residual monomer and has good transparency. By means of original equipment, the product in new trade mark can be stably produced, wherein the product has stable properties; correspondingly, produced ABS can satisfy user demands in the aspects such as flowability, tensile strength, bending strength, hardness, thermal distortion property, etc. The product can be extensively applied to downstream steps.