Taking the typical branching channel in Taihu basin as an example, a 2-D hydrodynamic model of river channel was constructed to study the main influencing factors and mechanism of flow diversion ratio in plain river networks, and a prediction equation of diversion ratio for plain river networks is established by ridge regression. The results show that the flow diversion ratio of plain river networks has a positive correlation with roughness, ratio of the width of the tributary to that of the main Channel and water level difference, while a negative correlation with the main stream discharge, and a complicated relationship with the branching angle. The discharge of the main stream and the ratio of the width of the tributary to that of the are two dominant factors of the flow diversion ratio. The multi-factor comprehensive prediction equation for the flow diversion ratio of plain river network can be used to predict the flow diversion ratio of braided rivers in plain river networks.