The chip flow interference is widely found in metal cutting processes. The existence of chip flow interference can deteriorate working environment of the cutting tool and increase cutting force significantly. However, chip flow interference has not received enough attention when researchers established mechanistic models for predicting cutting force with complex cutting tools. In view of this problem, 20 groups of cutting experiments were designed to evaluate the effect of chip flow interference on main cutting force. Test results show that the effect of chip flow direction interference on main cutting force is obvious. The maximum increasing rates of main cutting force caused by chip flow direction interference are 56.4%, 54.7% and 47.4%with cutters having 10°, 0° and –10° rake angles respectively. In addition, models for main cutting force considering chip flow interference are established. Finally, designed cutting edge inclination angles can decrease chip flow interference as well as main cutting force for more than 10%.