Interface velocity of a 3-D liquid film can characterize the overall flow properties of annular flow more accurately. However, few investigations have been conducted to perform the interface velocity measurement. In this article, on the basis of the scanning laser-induced fluorescence (SLIF) method, a velocity measurement principle of forward transcendence and backward encounter is proposed to measure the interface velocity of a 3-D liquid film. For similar image retrieval, an advanced feature extraction method, an improved weighted hashing algorithm, and the image similarity measurement method are developed sequentially. Furthermore, the interface velocity measurement is realized and the distribution of interface velocity is investigated comprehensively. It is concluded that as the liquid Reynolds number increases, the probability density function (pdf) of interface velocity shows the unimodal distribution, the bimodal distribution, and the flat distribution in sequence, corresponding to the transformation between the turbulent flow region, the transition region, and the fluctuating turbulent flow region. Moreover, Skewness and Kurtosis are employed to quantify the asymmetry and flatness of interface velocity distributions under the different flow regimes. Besides, the interface velocity fluctuation is analyzed, and the data frequency of interface velocity is determined as the dominant influencing factor. Finally, the average interface velocity is investigated and predicted, and the mean absolute percentage error (MAPE) is 4.40%. The interface velocity measurement method and the research results are helpful to the in-depth investigation of annular flow in industrial applications.