The spline sheath can not be processed by cutting for its shape，and the electrolytic process has to be adopted，so that the productivity is very low, precision and service life of the gears are very bad，and the depleted electrolyte pollutes environment. A practical die structure was presented for cold extruding the spline sheath in this treatise. It described on the important points of the die design and the operating principle of the die. The punch was fixed by a spring clamp sheath, so that the die was good coaxial and convenient for exchange of the punch. There were a rejecter and a stripper on the bottom die, the forge piece could broke away from the punch die and concave as soon as the extruding was over.Material utilization ratio, production efficiency, precision and mechanics performance of the workpiece are evidently advanced compared with the electrolytic process.