Abstract: Water level and flow velocity are two critical factors for flood control and forecasting. However, to our knowledge, there are few universal models that have been able to simulate water level and flow velocity effectively especially in the river channels without observed discharge data or stable stage-discharge relationship. In this study, the derivative expression of the friction is proposed using dimensional analysis based on water balance equation and force equilibrium equation. Then, the bi-variable (water level and flow velocity) coupling model is established by solving the derived differential equation. The developed model is tested in four river reaches in the Qiantang River, the Ganjiang River, and the Guijiang River. Our results indicate that the model can provide good simulations of water level in the study area (with coefficient of determination larger than 0.7 during both calibration and validation processes). This study also confirm the rationality of the model structure and its effectiveness in simulating the river flow.