The surface quality and contouring accuracy of die cavities directly influences the surface roughness of the products. Different types of complex surfaces of products have become popular in product design in recent years and consequently 5-axis machining techniques become a mainstream in the manufacturing of the die and moulds used in products mentioned above, because of their features and flexibility. This research applies Taguchi method to find out a set of optimal machining parameters in five-axis milling process. The table rotating-tilting type five-axis machine is used to perform the experimental cutting. The cavity of die is modeled as convex half spherical surface, and the material of die is NAK 80 die steel. The four parameters studied are cutting speed, feed rate, tool paths, and contact points, and each of these factors has three levels. The target of this study is the feature of smaller-the-better that is minimization of the surface roughness. The experimental results show that the optimal parameters are moderate cutting speed and contact points, higher feed rate, five-axis tool path. ANOVA analysis indicates that the tool path influences the surface roughness most, which accounts for about 86%. Using optimal parameters to machine a roughly machined concave spherical surface can reach its roughness to 0.234μm, and the roundness error about 0.0314mm. It is believed that the results and method presented in the paper give a good reference for industry applied.