Abstract: Plan Environmental Impact Assessment(PEIA) of coal mine area is a new work compared with other fields,therefore no technical guidelines can be followed;the assessment agents conduct the assessment work with various techniques and methods.Taking the PEIA of typical coal mine areas(Yulin-Hengshan and Yulin-Shenmu coal mine areas) in western China as examples,using the theories of hydrogeology and water resources as well as the basic method of EIA,an assessment method of underground water in the PEIA of coal mine area is offered in this paper.It is considered that the shortage of water resources and the friability of ecological environment are the common feature of coal mine areas in western China, "three water" balance is the foundation of the assessment,and to control the impact of coal mine areas development over water resources within the capacity of regional water resources is the key to the sustainable development of the coal mine area.