The invention discloses an extruding and upsetting die, an extruding and upsetting processing method and a magnesium alloy central jacket and relates to the technical field of plastic forming. The extruding and upsetting die is suitable for industrial production of large-scale and high-strength-plastic rods. In the extrusion process, the die exerts the effect of two refined crystal grain processesof conventional extrusion and upsetting; and the former is realized by reducing an inside diameter of an inner cavity of the die, and the latter is realized by the upsetting process of changing a diameter of a sample into a required size from a small diameter under the effect of a reverse extrusion force exerted by a prefabricated body placed in advance. The large-scale and high-strength-plasticrods can be prepared with the extruding and upsetting die and are suitable for the rail transit industry, the automobile industry, the exerciser industry, the numerical control machine tool industry and the like. The magnesium alloy central jacket is obtained through processing with the extruding and upsetting processing method. The magnesium alloy central jacket has the characteristics of low density, excellent vibration reduction and noise reduction, high cutting speed, high cutting precision and the like; and meanwhile, with micro-arc oxidation and electrophoresis surface treatment, the service life of the magnesium alloy central jacket can be guaranteed.