The stability model was established and the two-dimensional and three-dimensional lobes were plotted for the milling of lateral walls in order to avoid chatter occurring in the milling of lateral walls. The combination of milling parameters of free chatter can be selected in the stable zone of stability lobes. The stability of milling lateral walls influenced by radial depth of cut and teeth number of the milling cutter was analyzed. It is shown that the stable zone of stability lobes expands gradually as the spindle speed increases. The stable zone become wider as the radial depth of cut increases. The axial depth of cut limits is increased and higher productivity can be obtained as the teeth of the milling cutter decreases.