A differential cross shaft external grinding clamping novel structure comprises a main shaft faceplate, a main shaft center, a tailstock centre and a differential cross shaft provided with four equal circular shaft necks. Two ends of two equal circular shaft necks which are centrosymmetric and located before and after are respectively in press fit with the main shaft center and the tailstock centre. A limit rod which stretches to the rear side of one equal circular shaft neck on the upper portion of the structure is arranged on the main shaft faceplate. Each time a grinding wheel of a grinder grinds one equal circular shaft neck which is in center press fit with the tailstock centre, the limit rod plays a role in limiting the differential cross shaft not to rotate, after one equal circular shaft neck is grinded, the tailstock centre is loosened, and the differential cross shaft is rotated and clamped between the main shaft center and the tailstock centre to grind. A fixture is canceled when the differential cross shaft excircle shaft neck is grinded, the limit rod is directly utilized to position the differential cross shaft, rotation in the grinding process is avoided, and clamping is more convenient, auxiliary time is shortened, production efficiency is fully improved, and labor intensity of workers is lightened.