An approximate far-field boundary condition utilizing a source-sink idea for the rotor and the simple momentum theory were applied to the Navier-Stokes flow analysis around a horizontal-axis wind turbine. An iterative procedure was set up to apply this boundary condition to the flow with natural wind. Through computational tests for various distances of far-boundary, it was found that applying the approximate far-field boundary condition generally improves the accuracy of numerical solutions and computational efficiency. The solution becomes more accurate as the approximate boundary condition was applied to smaller far-field boundary.