Cutting performance is one of the most important factors to judge the NC machine tool, therefore it should be considered at the design stage. A structure design method by coupling the dynamics and cutting performance was investigated in order to promote the overall performance of a 4-axis milling machine developed by the laboratory. Combining with the chatter theory in machining, three dimensional chatter stability (spindle speed - width of cut – depth of cut) and chatter frequency (spindle speed - width of cut – chatter frequency) were predicted after acquiring the frequency response function (FRF) at the tool tip and cutting coefficients from the experiments. Next, experimental modal analysis was employed to test the machine. The roots of chatter occurrence, which was resulted from the inappropriate design, could be figured out after obtaining the visualized mode shape of the machine. In the end, the parallel spindle head of the machine was modified and the tool tip FRF comparison shows that the dynamic stiffness of the target mode is improved 28.2%, which is beneficial for the chatter resistance.