Abstract: The chemical characteristic and its formation of the coal acid mining drainage are discussed in this paper based on the spot investigation,samples examination,applied the correlation analysis method,and combined with the geology and hydrogeology background information.Coal AMD formed in the specific substance and environment condition.And when the condition is meet,the AMD can be produced in both high or low sulfur in the coal.Low pH and high Eh,TDS,hardness are the important characteristic of coal AMD.There are good relation between SO 4 2- and EC,Fe 3+ /Fe 2+ radio and Eh.Some trace elements and harmful heavy metal such as Ni、Cu、Co、Zn in the AMD come from pyrit dissolution while some others like Pb、Sr are mainly come from the AMD eluviation to the coal and rocks.