Sluice gates are widely used for flow control in open channels. This study shows that numerical tools using the Reynolds averaging Navier-Stokes equations are sufficiently advanced to calculate the contraction and the discharge coefficients, and the pressure distribution for free flow past a sluice gate. The trend of the existing inviscid theoretical contraction coefficient is quitedifferent from existing experiments. As the gate opening rate increases, the contraction coefficient for the present study gradually decreases if the gate opening rate is less than 0.4 and increases when the gate opening rate is larger than 0.4, exhibiting a tendency similar to existing experimental data. This is because energy losses by friction and water surface oscillations increase as the approach velocity from the gate increases as the gate opening rate is larger than 0.4. The discharge coefficients and the pressure distributions from the present analysis correspond closely to the existing experimental data. In this study, by performing a numerical analysis that does not use the assumptions adopted in the existing potential flow theory, the contraction coefficient, the discharge coefficient, and the pressure distributions were thoroughly analyzed. This study shows that existing numerical models using RANS are a useful tool in the design of hydraulic structures.