Based on the geometrical theory of the form milling the spiral taper gear, the computational formula of the cutting thickness and cutting width in every time was deduced. The milling force model for form milling the spiral taper gear was presented. The milling force factors were calibrated via single factor experimentations and the form milling force simulation programs were prepared. Experimental installations were designed to validate the availability of the milling force model. Comparison between the computational results and experimental observations confirmed the validity deviation of the proposed model was within ±15%.