The experimental studies of the flaring gate pier applied on the surface spillway in a high-arch dam show that a shock-wave will appear when the pattern of the flow is kept as super-critical.Meanwhile,the water depth at the outlet increases significantly,the flow moves downward in different directions,and the plunging jet is in a narrow and long shape,with a full longitudinal diffusion.In addition,the variation of the flaring gate pier design parameters affects little the discharge capacity of the surface spillway,these parameters including the contraction ratio β,the contraction angle α and the spillway chute angle θ.The pressure on the bottom of the spillway increases along the way and reaches the maximum before the outlet,and then decreases rapidly.Due to the flow impacting,the pressure on both sidewalls increases abruptly at the turning line of the flaring gate pier.To see the characteristics of the flow in the flaring gate pier,a simple calculation method is suggested based on the conversation of energy and mass,and the calculation methods for the jet trajectory and the horizontal length in air are also proposed.The results are found in good agreement with experimental data.