Abstract: In this paper, a hybrid indicator is proposed to determine the best grading scale of wavelet de-noising. The variation rule of the root mean square error, signal to noise ratio and smoothness with regard to the decomposition scale is employed to develop the hybrid indicator. Different characteristics in the process of wavelet de-noising are considered to define the hybrid indicator, and the best decomposition scale can be determined by identifying the inflection point of the hybrid indicator. A series of experiments on different signals are utilized to test the effectiveness of the hybrid indictor. The comparisons with current methods are further used to demonstrate the advantages of the hybrid indictor.