This paper focuses on developing an empirical model for the prediction of milling forces in high-speed end milling of P20 die-mold steel. The spindle speed, feed rate, axial and radial depth of cut are considered as the affecting factors. The data for establishing the model are derived from high-speed end milling experiments conducted on a 5 axis machining center according to the principles of DOE (design of experiments) method. The influences of milling parameters on milling forces are investigated by analyzing the experimental curves. Consequently, multiple-regression analysis is applied in developing the empirical model. Furthermore, the significances of the regression equation and regression coefficients are statistically tested in this paper to validate the model.