The invention provides a design method of a straight toothed spur gear cold extrusion shaping die, and belongs to the technical field of shaping dies, and the method comprises the following steps: determining the plastic deformation of cold extrusion shaping; determining a mathematical model of the elastic deformation of the shaping female die; determining a mathematical model of the elastic recovery amount of the gear blank; determining a mathematical model of the total deformation of the cold extrusion shaping; determining a calculation formula of geometric parameters of the shaping female die; and calculating geometric parameters of the shaping female die. By using the design method of the straight toothed spur gear cold extrusion shaping die, the geometric parameters of the full toothform of the shaping female die used for cold extrusion shaping can be rapidly determined, the plastic deformation of the gear blank, the elastic deformation of the shaping female die and the elastic recovery of the gear blank are comprehensively considered, and the improvement of the cold extrusion shaping precision of the target gear is facilitated.