Rubber dams are hydraulic structures that are constructed on rivers which are cheaper than similar structures. In this research, rubber-dam modeling was performed by 3 different pressures inside the tube (1.5 to 3 KN/m²) and 3 discharges (1.5 to 5.5 lit/s) by Flow-3D software. A rubber dam, located on an open channel, was verified using an experimental model. The correlation coefficient resulted from fitting numerical model results and physical quantities, was 0.9357, which represents high accuracy of the numerical-model results. Maximum discharge coefficient was about 0.46 in discharge of 5.25 lit/s and pressure of 3 KN/m². It was revealed that 100% increase in internal pressure of the tube leads to 5% increase in discharge coefficient. While, the same amount of discharge increase will lead to an increase of more than 25% in discharge coefficient. The H/D_h parameter was recognized as one of the effective factors on discharge coefficient. The modeling results showed that 31% increase of this parameter will increase discharge coefficient by 70%. Also, effective factors on flow velocity through the rubber dam were evaluated.