Abstract: Riverbed structure in mountainous rivers is the product of the interplay between flow-sediment and riverbed, which determines the magnitude of riverbed resistance and significantly affects the bedload transport. In order to characterize the details of riverbed structure, this study proposed four new dimensionless parameters (concavity-convexity number, average concavity, average concavity, and concavity-convexity) of riverbed structure characterization and their calculation methods based on the topographic survey datasets of seven sections of the main stream and tributaries of Xiaojiang River (a tributary of Jinsha River in the upper Yangtze River) in April and September 2017. The calculation method of four new parameters is simple and intuitive. Four parameters represent the development degree of the riverbed structure and morphological characteristics of riverbed structure. Moreover, the characterization of the concavity and convexity is more distinguishable if the degree of the riverbed development is relatively lower. The results based on the application of the new method show that the bulge of the riverbed structure in the lower reaches of the Diaoga River, Taojia Creek, and Qingshui Creek is relatively high and convex, i. e., the deep and steep depression, high resistance of river bed, and low sediment transport rate. However, the upper reaches of the Diaoga River, Xiaojiang River, and Jiangjia Creek, and Lanniping Creek, the bulge of the riverbed structure is relatively low and flat, i. e., the shallow and gentle depression, low resistance of river bed, and high sediment transport rate.