In order to improve the precision of wavelet ridge extracted by modulus maximum method based on scalogram, a new method for extracting wavelet ridge based on optimal reassigned wavelet scalogram is proposed. Firstly, Morlet wavelet is optimized and reassigned wavelet scalogram is utilized to improve time-frequency concentration of the scalogram. Then, singular value decomposition (SVD) de-noising is applied to the reassigned wavelet scalogram to reduce the influence of the noise. Finally, wavelet ridges are extracted by modulus maximum method and the instantaneous frequency of signal is obtained. The results of experiment and engineering application show that the proposed method is feasible and effective for extracting feature of mechanical vibration signals with low signal-to-noise ratio (SNR).