In this study, the experiment for scale model of tunnel and the three-dimensional numerical simulation for real tunnel were performed to analyze the effect of natural wind on the resistance of ventilation in accordance with tunnel conditions (length, gradient and form of pit-head). The validity of the numerical simulation method was verified by the experiment of scale model. The three-dimensional numerical simulation for real tunnel led to the result that the average air velocity in tunnel was changed by length, gradient, form of pit-head. Therefore, the design standard for average air velocity in tunnel by natural wind has to be revised. At the design of tunnel ventilation, it is considered that it has to be applied to the purpose in accordance with tunnel condition.