In order to study the impacts of different width-depth ratios and radius-width ratios on the hydrodynamic characteristics at open-channel confluences with bend flow, a three-dimensional numerical model was established by using the volume of fluid (VOF) method for the free surface capture and adopting the RNG k-ε model for the governing equations closure. The water surface pattern, velocity distribution, secondary flow and shape of separation zone were analyzed after the simulations of five combined cases with three width-depth ratios and three radius-width ratios. The results indicate that the degree of water level drop near the intersection decreases with the increase of the width-depth ratio or the decrease of the radius-width ratio. Compared to the radius-width ratio, the width-depth ratio has a stronger impact on the non-uniformity of velocity distribution at the confluence and the downstream area. When the width-depth ratio increases, the longitudinal flow rate increases and the non-uniformity of velocity distribution increases with enhanced flow deflection effect. When the width-depth ratio or radius-width ratio increases, the reflux structure at the bend is enhanced, the size of the separation zone increases with narrower and longer horizontal form.