It is very important to develop a more effective and objective method to get more quantified information of coherent structures from the turbulent signal. Based on wavelet and bi-spectrum analysis, a reasonable method was put forward. The large eddy signal including the information of coherent structures was extracted by the bi-spectrum and cross correlation analysis, and multi-scale coherent structures were detected by the wavelet transform. Besides, by using wavelet analysis, a new identification criterion of energy-containing scale was established. The reliability and rationality of the method was verified by an example with the sample data from the experiment on the mechanism of rib-lets drag reduction. Furthermore, this research has also led to the conclusion that the multi-scale characteristics of coherent structures can be gotten by the above method.