Gun steel is an important weapons material. This paper studied the relationship between law cutting conditions and milling force, in order to improve the machining accuracy and surface quality of gun steel. The influence law of several factors on the milling force were discussed by orthogonal experiment method, and the simulation model of milling force are established. The milling force empirical formula is concluded, the formula contains cutting depth, cutting speed and every tooth feed. The cutting force is measured using a three-to-force measuring instrument 9257B at the machining center. The same milling force distribution data is given, using the method of numerical calculation. The results showed milling force simulation model is accurate and experimental data are credible. This research method has certain reference value to the research of metal cutting theory, material processing technology and the optimization of the cutting process. Keywords: gun st