Abstract: In operation of the Longtouqiao reservoir spillway, serious phenomena of water crown and deflected flow occurred in the chute section behind the gate pier. Aiming at this problem, physical model tests and numerical modeling were conducted in this study to simulate the 3D flows on the spillway, using an RNG k-ε turbulence model, modified SIMPLE algorithm, and VOF model. Comparison shows that the numerical calculations of hydraulic characteristics agree well with the model test results, including spillway capacity, water surface profile, flow velocity, and pressure on the weir. And the simulations can well describe the locations and behaviors of the water crown and flow deflection. To improve the flow regime, we optimized the thickness of the gate pier and its tail shape through examining a set of modification schemes, and achieved satisfactory results that were verified by the model tests and numerical simulations.