Abstract: A wavelet ridge method to analyze chotic motion was described and applied to analysis of nonlinear vibration of a blooming mill having chaotic motion. The wavelet ridge distinguished periodic motion, quasi-periodic motion, or chaotic motion by analyzing the time history of one component of the system state variables. Compared to other methods, such as Poincare´ sections or phase diagrams, wavelet ridge was more suitable to high dimensional chaotic systems. In addition, the clutter of instantaneous frequency represented by the wavelet ridge can distinguish between strong and week chaotic motion. The wavelet ridge method also provided more accurate partial details and features of chaotic motion.