A possibility of the drag coefficient estimation in numerical water basins was discussed where the numerical solution were calculated by the 3-dimensional hydro-dynamical model (FLOW-$3D^{(R)}$) with the RNG $k-{varepsilon}$ turbulence model. On the known cases of the drag coefficients for a rectangle, the numerical drag coefficients got $1.34{sim}1.52$ and the wind tunnel values were $1.3{sim}1.5$. For a cylinder, the numerical values were calculated as $0.75{sim}0.78$ in the range of 0.5<h/D<3.5. Therefore the numerical results showed a good agreement with the physical experiment in a cylinder body runs. On the unknown cases of a row of rectangle, the drag coefficients were more increase than the cases of single body because of the interaction of other structures. And also the drag coefficients had large values as the distance interval ratio of the structures more and more decrease.