The effect of aerosol fine particle(PM_2.5) on the visibility was discussed,and the relationship between PM_2.5 and visibility was established theoretically.The relative PM_2.5/PM₁₀ and extinction coefficient were analyzed with changing of particle distributions based on Mie scattering theory.By comparison of measured data and calculated values,experimental results indicate that the pollution of PM_2.5 is the main factor that results in visibility dropping,and the error of calculated value is less than 30%,which is significant for dealing with pollution of PM_2.5 and improving atmospheric visibility.