Abstract: Evaluating the emission reduction effectiveness of porous fence especially for PM_2.5 scientifically is meaningful for directing the optimization design of porous fence and the acceptance of porous fence facility.A novel method was proposed to evaluate PM_2.5 emission reduction effectiveness of a porous fence to an open coal stockpile.An open coal stockpile and the wind condition of a month in a literature were employed and a computational fluid dynamics software Fluent was employed to calculate the maximum wind velocity in front of the stockpile with and without porous fence.The data of maximum velocity and wind conditions were put into the formula of emission calculation for PM_2.5 recommended by US EPA (United States Environmental Protection Agency) to calculate the PM_2.5 emission of the stockpile.The results indicated that the emission reduction efficiency of plane porous fence with 40% porosity reached up to 99.33%.In order to validate this method, the condition of this method was put into another method.The results of those two methods were in well agreement.