Abstract: Granularity distribution,microstructure,particular type and heavy metals such as As,Se,Cd,Pb,Cr and Be in fly ash were studied under different particle diameters for fly ash from Xiaolongtan Power Plant.With the reduction of granularity,quantities of global particulates were decreased,but quanitities of non-global particulates were increased.The surface of most PM_2.5 was not smooth,and the phenomenon of particles adsorption existed among different grain sizes.The contents of heavy metals,such as As,Se,Cd,Pb and Cr,were enriched in fine particles with diameter below 2.1 μm.Fly ash of high calcium had a strong adsorption on As.