In the natural fluvial systems, the shape attribute of particles can reflect their source, transportation, and deposition processes. For a long time, the sedimentologic community lacked relatively uniform quantitative and multidimensional particle shape parameters. This study aimed to quantify particle shape of modern sands, find a better shape characterization, and advance the understanding of shape properties in sedimentary grains.Methods: Taking the Parlung Tsangpo as an example, Tibet, a tributary of the Yarlung Tsangpo, computer- aided technologies such as image analysis and software analysis were used to identify the detritus composition and quantify the shape parameters of 2276 particles in 8 river sand samples. The shape signals of these grains were processed using statistical methods such as principal component analysis and factor analysis.Results: Eleven particle shape parameters were evaluated, and 3 shape signals, including circularity factor, regularity factor and smoothness factor, were extracted and defined by factor analysis.Conclusions: These parameters can be used to characterize particles by the degree of circularity (macroscopic shape), contour regularity, and contour smoothness at the meso scale. Their relationship with the particle composition and size was thus further explored. The results of this study provide important references for interpreting the shape signals of particles in fluvial systems, understanding their microscopic properties and external physical processes.