The leaching experiments of four kinds of broken gangues with different particle diameters from Pingdingshan coal mining region were carried out to simulate the impact of gangue filled in mined-out area on the underground water environment, in which the leaching solution's pH value,conductivity total hardness,and F,Zn,Mn,Cd,Cr,Cu and Pb contents were measured.Under the condition of experiment,in the leaching solution,the contents of F and Mn exceeded the standards,Pb can be detected occasionally and pH value is on the high side of the standard,so the leaching solution may pollute underground water.The experiments showed that the smaller the particles of gangue are,the easier the leaching is,the contents of other heavy metals were very few and even cann't be detected,gangue does not belong to dangerous solid waste,and gangue filling is possible when strict control measures are adopted.