Abstract: The present disclosure proposes a system and method for measuring particle size distribution of sediment grains. The method includes: acquiring a first sediment grain image and a second sediment grain image; processing the first sediment grain image to obtain a sediment grayscale image; obtaining a depth image based on the sediment grain images, and obtaining a depth grayscale image by processing the depth image; based on the depth grayscale image, generating a preliminary region mask; cropping the sediment grayscale image using the preliminary region mask; obtaining an image with first-stage clustering results by performing cluster analysis on the cropped sediment grayscale image; obtaining an image with second-stage clustering results by performing cluster analysis on the sediment grains with a particle size smaller than a preset threshold in the image with first-stage clustering results using a DBSCAN; obtaining the particle size distribution result based on the image with second-stage clustering results.