Abstract: Windbreak nets are the primary measure for reducing wind in outdoor areas and are widely used. In order to explore the shielding effect of windbreak nets, wind tunnel tests were conducted on a butterfly-shaped windbreak net with 45% porosity. The variation of wind speed reduction coefficient with shielding distance was studied, and a quantitative evaluation index, the wind reduction coefficient, was introduced. The results show that the wind speed reduction coefficient decreases first and then increases with the shielding distance, with the better shielding effect achieved at a shielding distance of 6H. The better wind reduction zone is within a range of 6 to 8 times the net height. The shielding distance of the 45% porosity butterfly-shaped windbreak net exceeds 30H. Wind speed has little effect on the shielding effect of the windbreak net. The wind reduction effect coefficient indicates that the butterfly-shaped windbreak net can overall reduce the wind speed within the range of 1H net height and 30H coverage distance by 44%. It is not the case that the closer the sheltered area is to the windbreak net, the better the wind protection effect. Two models of wind speed reduction coefficient distribution along the vertical and the downwind directions have been proposed, which can quickly estimate the wind reduction effect of the windbreak net. The research results have reference significance in determining the height of the windbreak net and the distance between net piles.