Coarse particle vertical pipeline hydraulic transport has been widely used in deep sea mining, petrochemical industry and shaft slag removal. The precise measurement of the velocity of coarse particles within a solid–liquid two-phase flow in a vertical pipe constitutes a pivotal and challenging aspect when investigating particle motion characteristics. We introduce a method for measuring coarse particle velocity that combines a GMM motion detection model with flow direction constraint matching. In this approach, a high-speed camera system captures the flow image of solid–liquid two-phase flow within a pipeline, and the GMM model analyzes the image to detect the motion particles. Subsequently, a rapid particle matching algorithm, incorporating flow direction constraints, is formulated to establish the particle matching relationships. Simulation and real experiments substantiate the efficacy of this method. Moreover, the method achieves high-precision matching with an accuracy of up to 99%. For videos captured at 30 frames per second (fps), the method enables real-time speed measurement, with an overall measurement error of less than 5%. In summary, this is an effective method for measuring coarse particle velocity field which is important to the study of the motion characteristics of solid–liquid two-phase flow.