Abstract: On the basis of the experimental study, two-phase flow pattern of the narrow rectangular channel by the way of wavelet analysis was identified effectively. An effective way to recognize flow pattern without visible case or high-speed photography was provided. By the visual observation, it is found that there are four flow patterns (bubble flow, slug flow, churn flow, and annular flow) in the narrow rectangular channel. The power density spectra of the four flow patterns were shown according wavelet analysis. The frequency distribution of each flow range and maximum energy distribution were also defined. Therefore, using the frequency distribution and the energy distribution maximum value can identify and determinate flow pattern effectively.