For the problem of insufficient corner filling and excessive forming loads in the process of cold extrusion for rectangle spline, x1 (diameter of billet), x2 (billetinitial chamfer) and x3(die semi-angle) were selected as optimization variables, and the multi-objective optimization of cold extrusion process parameters was studied by the response surface method (RSM) combining with finite element method (FEM). Then, the second-order response surface models of two objective functions were established based on the experimental design result. The variance analysis results show that the above models are of high prediction accuracy, two objective functions related to response of design variable are described clearly. Thus, the optimal process parameters of forming rectangle spline shaft are obtained as x1=Ф48.5 mm, x2=35° and x3=30°. The optimized process parameters were verified practically. The result shows that  the tooth tip collapse angle reduces to 0.27mm and the maximum forming force reduces to 1300 kN. Experimental result shows that the qualified products can be obtained by multi-objective optimal process parameters.