Nitriding is one of the most efficient methods used to enhance the service life of aluminum extrusion dies. In this paper, a new nitriding process has been introduced that is characterized by that 4Cr5MoSiV1 steel, a typical material used for extrusion dies, was nitrided by using two-stage nitriding process. The microstructures of nitrided layer have been analyzed by means of optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and microhardness (MH). The results show that pre-heat treatment on the 4Cr5MoSiV1 steel extrusion die can be carried out under the condition of quenching at 1040 °C, double tempering at 600 °C and 560 °C for 2 hours each. Operating parameters of two-stage nitriding are set as follow: stage one, 520 °C for 6 hours, the flow rate of NH3 of 0.6 m3/h; nitriding pressure of 453 Pa and stage two, 580 °C for 8 hours, the flow rate of NH3 of 0.35 m3/h; nitriding pressure of 453 Pa.