Abstract: A river crossing bridge may induce backwater owing to the flow resistance generated by its piers, which may consequently affect river flood discharging. In the field of bridge and culvert hydrology, a large body of previous studies concerns backwater calculations for the bridges orthogonal to river channel, but still lacking are the theories or empirical formulas applicable to oblique river crossing bridges that involve complicated flow structures beyond their applicability. This study develops a mathematical model for the two-dimensional depth-integrated flows to simulate bridge backwater, and verifies it through a flume experiment. Based on numerical simulations, hydrodynamics and characteristics of the backwater in river channels with oblique crossing bridges are examined, focusing on analysis of the maximum backwater height varying with bridge pier size, crossing angle, and inflow velocity in the cases of flow blockage factor in a range of 10% - 40%. Simulation results show that at a fixed blockage factor, the maximum backwater height increases and then decreases with the increasing oblique angle. Oblique crossing may induce a deflection of the river flow, leading to significant asymmetry of the velocity distribution.