The utility model relates to a connecting device, in particular to the upper buckle auxiliary apparatus of an oil pipe hanger used for an oil pipe hanger and the upper buckle of a double metric short pitch arranged at the lower portion of the oil pipe hanger. The upper buckle auxiliary apparatus of an oil pipe hanger comprises a mandrel, a thrust collar and a locking ring. The mandrel is divided into a left segment, a middle segment and a right segment. The external diameters of the left, middle and right segments are successively decreased. The middle segment is screwed with the thrust collar and the locking ring. Due to the adoption of the upper buckle auxiliary apparatus, the problem that the connection of the upper buckles of some oil pipe hangers can not be realized through a hydraulic buckle screwing machine due to the reasons that the clamping parts of the oil pipe hangers are unreasonable in design and machining, or the dimensions of the external diameters of the clamping parts, and the dimensions of the pitch diameters of double metric short pitches connected with the lower portions of the oil pipe hangers are not matched with the designed clamping scope of the hydraulic buckle screwing machine, is solved. Meanwhile, the torque of an upper buckle of an oil pipe hanger and a double metric short pitch is ensured. Therefore, the upper buckle auxiliary apparatus plays a key role on the safety usage of an oil pipe thread.