According to the study of high speed milling force of difficulttomachine material Ti6Al4V(TC4),with multifactor orthogonal experiment, the influence of cutting parameters on milling force was analyzed and a method about high speed small feed milling can be applied in the difficulttomachine materials. Cutting force in milling process was divided into vertical milling force, horizontal milling force and axial milling force. According to the relationship between the machining parameters and the milling force, three directional milling force model was established by using probabilistic statistical method such as least square method and regression analysis theory. The regression parameter significance test was carried out on the milling force model,and the confidence and residual error of the model were analyzed. The results show that the established milling force model can accord well with the original experimental data and the reliability is good, so it can be used for prediction and control of milling force and provide reliable basis for parameters optimization of high speed milling of titanium alloy.