Using a navigation-obstructing section downstream the Xiangjiaba Dam of Changjiang River as a research object, a two-dimensional unsteady fractal mathematical model that can meet the requirement for maintaining a minimum water depth was established for statistical analysis of the channel width, and the fractal dimension of the river channel’s transverse section was calculated, demonstrating one-order fractal dimension characteristics. The results show that the fractal dimension of the channel width has a close relationship with the water depth, the topography of river reach, and the shape of transverse section, demonstrating a general increasing trend of the fractal dimension of the channel width with the increasing water depth for a shoal and a general decreasing trend of the fractal dimension of the transverse section with the increasing flow velocity. Comparison of the fractal dimension of different shoals in the same river reach shows that the fractal dimension is relatively small for a transverse section with smooth topography under the same flow rate from upstream.