Abstract: The nonlinear dynamic behavior of a vibration system affected by dry friction is investigated in the paper. In order to capture accurately dividing points, the theoretical method about the points which separates slip phases from stick phases is expounded, and stick-slip vibration induced by dry friction is analyzed and Lyapunov exponent is used to investigate the stability of the system. The dynamic responses of a two-degree-freedom vibration system with dry friction and the routs from periodic motion to chaos are analyzed by numerical simulation.