Abstract: Since 2013, a branching channel has been formed in the Yellow River mouth, which diverted the river water discharge to the sea. However, the diversion characteristics of the branching channel and its influencing mechanism are not clear. A three-dimensional hydrodynamic numerical model of the river mouth was constructed using the Delft3D model. The diversion processes in different cases were simulated and the controlling factors were examined. Results show that the asymmetry of water discharge in the branching channels decreased with the increase of the river water discharge. The increase in river water discharge increased the water level gradient between the eastern and northern channels. As the result, the increase in water discharge in the eastern channel was greater than that in the northern channel, which alleviated the asymmetry of water discharge in the two channels. Tidal force amplified the asymmetry of the water diversion in the two channels. However, the tidal amplification decreased with increase in river discharge. This is due mainly to the differentiation in water level gradient between the two channels under the influence of the semi-diurnal tide in the river mouth, which promoted the seaward flow in the northern channel, but inhibits it in the eastern channel.