As the instantaneous flow of bulk materials is hard to be accurately measured at a high speed on a large capacity belt conveyor in real-time, a more positive and accurate method to measure the material instantaneous flow on belt conveyor based on laser scanning technology was proposed. When the 3D laser point cloud data of bulk materials' surface profile are acquired at high speed by using 2D laser rangefinder and conveyor speed sensor, preprocessing steps of filtering, outliers excluding and data smoothing are applied. Then an automatic contour extraction method was proposed by analyzing the space morphological characteristics of material flow outline's laser point. By integrating the element area of material cross section, a mathematical model to calculate the instantaneous flow of bulk materials on belt conveyors was established. When measuring a trough belt conveyor whose belt speed is at 0.5 m/s to 2 m/s and bandwidth is 200 mm by using our laser scanning measurement system, the data repeatability and correlation can reach above 98%. Experiment results show that this method has strong applicability and reliability due to its small sample spacing, high measuring accuracy and real-time performance. The acquirement of real-time and accurate data can offer convenience for the further research of energy-saving control technology of belt conveyor in bulk terminal.