Chatter phenomenon often occurs during end milling of metal-cutting and becomes a common limitation to achieve high productivity and part quality. This paper studies the relationship expression between the parameters of oblique cutting and milling coefficients by analyzing the geometrical relationship of oblique cutting, and derives the mathematic expressions in theory between the cutter parameters and chatter. For the purpose of chatter avoidance, this paper studies the effect of helix angle and normal rake angle on milling stability under the condition of the same milling parameters, and plots the three-dimensional stability lobes of the spindle speed, axial and radial depths. It can be found that the milling stability is increased with the increment of helix angle and normal rake angle. Through the three-dimensional lobe, it is possible to choose the appropriate cutter parameters to reduce and avoid the chatter.