The invention relates to an internal thread end cover four-mode-driven synchronous-forming combined plastic injection mould and a processing method thereof. A static mould base is fixedly coaxially arranged at the inner side of a static mould plate, static moulds are embedded and fixedly arranged in the middle of the inner side of the static mould base; a main shaft hole connected with a hydraulic cylinder guide rod is formed in the middle of the outer side of a movable mould plate, a movable mould base is fixedly arranged at the inner side of the movable mould plate, movable moulds are embedded and fixedly arranged in the middle of the inner side of the movable mould base; the static mould plate is oppositely buckled with the movable mould plate, a plastic injection cavity is formed by jointing surfaces of the movable moulds and the static moulds, four plastic injection cavities are correspondingly arranged on the movable moulds and the static moulds, and are symmetrically uniformly distributed in the middles of the movable moulds and the static moulds, a rotating mould rod is coaxially arranged in the plastic injection cavity of each static mould, and the four rotating mould rods are driven by a synchronous drive device to synchronously rotate. The internal thread end cover four-mode-driven synchronous-forming combined plastic injection mould is simple in structure, reasonable in design, high in processing precision, simple in structure, long in service life, convenient to demould, and wide in application range, and has a good structure stability; the processing efficiency is improved, and the processing quality is effectively ensured.