Abstract: To explore the variation of grain size distribution in tidal flat under different suspended sediment concentrations, physical simulation experiments in flume were conducted for tidal flat of the Yellow River Delta. With the sediments （15 t） collected from the tidal flat surface in the field, an indoor flume was designed in a scaled-down size proportional to the real case, in which wave/tidal dynamic parameters were set, and the grain size distributions under different suspended sediment concentrations （0～14.9 kg/m³） were measured and analyzed. Results show that the characteristics of grain size distribution of tidal flat changed obviously with the decrease of suspended sediment concentration. With the decrease of sediment concentration, the distribution range of fine-grained sediments in the whole “tidal flat” decreased in a general coarsening trend; however, that of very coarse particles also decreased. Under different sediment concentrations, the average sorting coefficient, skewness, and kurtosis were generally greater in the upper intertidal zone than those in the intertidal zone and the lower subtidal zone, reflecting better sorting in the upper intertidal zone and the frontal subtidal zone than in the middle tidal flat. In addition, with the decrease in sediment concentration, the micro-topography of the “tidal flat” was gradually eroded and broken. This physical model experiment of tidal flat is able to reproduce quickly the variation in topography of erosion and deposition under different sand supplies and parameters, with which any changes of tidal flat under specific conditions can be simulated for better prediction in real cases as a reference for safe operation of human activities in similar tidal flat areas.