A new approach is proposed to model the milling force based on the cutting force shape characteristics in end milling. The relationship between the cutting force shape characteristics and the cutting depths is analyzed and milling forces are classified into 10 types according to the combination of cutting depths. Further, force indices are extracted and then the real cutting depths are detected based on the changes of force curve characteristics via the force indices in end milling process. Then, bring forward a method of modeling cutting force based on the different types, and the use of real cutting depth makes the model to be more accurately. More important, experiments designed on the classification of milling forces strengthen the pertinence, and makes the experiment data more reliable. The approach is validated through experiments on aluminum alloy 7050-T7451.