The invention provides a rotational molding process of a three-layer plastic automobile shell, which belongs to the field of rotational molding of automobile shells and solves the problem of poor performances of the automobile shell in the prior art. The rotational molding process for the three-layer plastic automobile shell comprises the following steps: manufacturing an external die and an internal die according to an automobile type; fixedly connecting the external die with the internal die through a locking device and forming an accommodating space by the external die and the internal die; adding a rotational molding powder material and a foaming granule material with different melting points in a cavity formed by the external mold and the internal mold; and performing rotational molding after closing the dies, so as to form an internal layer and an external layer of the automobile shell by the rotational molding powder material and form a foaming layer in the middle of the internal layer and the external layer by the foaming granule material. According to the invention, the three-layer plastic automobile shell is molded one time through the rotational molding process, so that the molding period of the automobile shell is shortened; and as a three-layer structure is adopted, the strength, the rigidity and the heat-insulating property of the three-layer plastic automobile shell are all increased compared with those of the automobile shell with a two-layer structure.