In a beach morphological process, such as a formation of a sand bar and a beach cusp, sediment sorting plays an important role. To describe a mechanism of sediment sorting directly, the movable bed simulator, which is a granular material model based on the distinct element method is used. In this paper, a hydraulic experiment using an oscillatory water tunnel is conducted to track motion of sediment particles under vertical sorting in sheetflow regime. The three-dimensional movable bed simulator is driven to track detailed motion of individual sediment particles numerically. Performance of the movable bed simulator as a tool of computational dynamics is shown by comparing simulated physical properties, such as series of instantaneous images, velocity pro. le and number-density distribution of sediment particles, with the result of the experiment.