The invention relates to an adaptor device for the synchronous butt joint of a main cone nut and a main cone flange of an automobile drive axle assembly. The adaptor device comprises an adaptor inner cylinder, a splitting gland and an adaptor outer cylinder; inner bores are formed on the adaptor inner cylinder and the adaptor outer cylinder; the shape of the inner bore of the adaptor inner cylinder is meshed with that of the outer diameter of the main cone nut; a cylindrical shaft shoulder is arranged on the middle part of the outer circumferencial surface of the adaptor inner cylinder; the outer circumference of the cylindrical shaft shoulder is matched with the inner circumference of the adaptor outer cylinder, so that the adaptor inner cylinder is embedded into the adaptor outer cylinder concentrically; and the splitting gland has a semicircular step structure and is fixedly connected with the adaptor outer cylinder, so that the adaptor outer cylinder is prevented from being fallenout of the adaptor inner cylinder and can rotate relative to the adaptor inner cylinder. The adaptor device has the advantage that: compared with the main cone flange needing to be fixed in the priorart, the main cone nut which is screwed tightly by rotating has better accurate control effect and higher work efficiency.