Abstract: We apply the friction loss equation to natural rivers in this paper. Using effective methods such as data analysis and data fitting, an analytical form of river resistance is obtained based on hydraulic geometries including slope, discharge, flow velocity, grain size, river shape parameter and so on. Through inversion of this river resistance law, the river shape parameter can be used as a discrimination criterion and two simple river pattern discrimination threshold curves with clear physical meanings can be constructed. The two curves divide the river systems into three main patterns: single-thread, stable multi-thread, and unstable multi-thread channels. Analysis reveals that in this method, a single-thread channel is sensitive to bank strength, but it is not true for a braided channel river, particularly those with an overlarge width-depth ratio. The pattern of a river can vary in a short period following an external disturbance as often does a meandering river with transient braided channels, but it could eventually return to the dynamic equilibrium state.