In order to evaluate the feature of flood discharge and energy dissipation of broad tail pier of surface spillway in the primary scheme of Dongzhuang project, the paper used RNG k-ε two-equational model for 3D turbulent flow and the VOF method to numerically simulate the feature of water flow of broad tail pier based on hydraulic model test. According to the primary scheme, the paper calculated discharge capacity, water surface curve, velocity, longitudinal length of water and impact pressure in the plunging pool, and compared the results of calculation and test,and found both the result are in good agreement. After the comparison of those values of model test and calculation,it shows the broad tail pier have affected the discharge of surface spillway No.2 under high water level; ΔPmax is under the protection standards of 15×9.81 kPa. The contraction ratio of preliminary design scheme is too large and, piers angle is small, the effect of longitudinal diffusion of water tongue is not obvious and is unable to realize the effect of no collision free energy dissipation in surface deep hole.