Abstract: If it is assumed that the flood and tidal waves in a tidal river are independent of one another, river stages can be considered as the superposition of bi-directional propagation, namely flood waves from the upstream and tide waves from the downstream. Based on the assumption, a bi-directional stage routing model (BSM) for a tidal river is developed according to the basic stage routing equation derived from the storage equation and the water balance equation. In order to prove the feasibility of the separation of flood and tidal waves, three tests are conducted by using the approaches of the ideal models to analyze the assumption, stability, rationality and validity of the BSM. The results show that the structure of the BSM is reasonable, and its performance is satisfactory.