The utility model relates to an adapter device for synchronous butt of a main cone nut and a flange of a car drive axle assembly, which comprises an inner adapter barrel, a split gland and an outer adapter barrel, wherein the inner adapter barrel and the outer adapter barrel are both provided with inner bores; the inner bore of the inner adapter barrel is in a shape meshed with the outer diameter of the main cone nut; the outer circumferential surface of the inner adapter barrel is provided with a cylindrical shaft shoulder in the middle; the outer circumference of the cylindrical shaft shoulder is matched with the inner circumference of the outer adapter barrel so that the inner adapter barrel is concentrically embedded in the outer adapter barrel; the split gland has a semi-circle step structure; and the split gland is fixedly connected with the outer adapter barrel to prevent the outer adapter barrel from falling off from the inner adapter barrel and enable the outer adapter barrel to rotate relatively to the inner adapter barrel. The benefit of the adapter device is as follows: a screwing manner by rotating the main cone nut has better accurate control effect and better working efficiency than the need of fixing a main cone flange in the prior art.