Physical models of speed-reducer shaft and dies were established by using UG/NX software.Based on Deform software and the selected rigid viscoplastic theory and shear friction model, the cold extrusion process of speed-reducer shaft was simulated. Then forming force, stress and strain at various stages were got and the diversion of center hole was analyzed in forming process. The metal flow and filling rules were also got. The results of simulation made good agreement to the model test and the correctness of the model and process rationality were varified and the measures to avoid unfill forming of center column were put forward. This research plays a guiding role in the simulation of the cold extrusion forming and control of the plastic forming technical parameters.