A porous wall model for wind tunnel analysis has been newly developed. To establish the model, flows through a hole were directly analyzed by a CFD method. The flow through the hole was computed in different flow conditions and hole shapes. From these computations, we formulated a linear relation between the flow rate and the differential pressure, including the effects of hole size and boundary layer thickness. This linear model is partially validated by an experiment. Then, we compared the computation result of a porous wall using the present model with that by a direct computation. It suggests that the present model has enough accuracy for the simulations of wind tunnel with porous walls.