The influence of radius ratio of cutting point and cutter on cutting force and stability during end milling process is presented in this paper. To derive motion equations, a 2 DOF mechanical model of end milling considering both regenerative and self-excited effects was established. Different ratio values during three milling conditions were analyzed. Cutting forces as well as stability under different radius ratios by changing curvature radius and cutter radius were elaborated respectively. The results show that when other parameters are set fixed, cutter with relative large radius has smaller cutting force and larger stable range. Cutters with same radius will overlap on cutting force when radius ratio is large enough even under different milling conditions. The proposed analysis on cutting force and stability can be used to determine the optimal parameters, such as cutter radius and spindle speed etc. to improve the accuracy and productivity.