Transport rate of windblown dusts such as soil, sand, snow is proportionate to U_*^3 and U_*, friction velocity, approximately to flow velocity of wind. Therefore, through measurement and the flow velocity of wind, it turned out that,considering different velocity distributions caused by downstream distance and porosity percent,windbreaks with appropriate porosity rate to the protection area should be chosen for the optimal fence effect. In the economic respect, better are fences with gap of 20%∼30%. Among the windbreaks to have the optimal fence effect.