This paper is the result of hydrogeological survey engineering.

Objective With the characteristics of wide distribution, concealment, heavy pollution, slow natural purification and long duration, the "goaf water" of coal mine has become an important restrictive factor that seriously threatens the construction of ecological civilization in China in the post coal mining era.

Methods Taking the goaf water of coal mine in Shandi River Basin of Yangquan City, Shanxi Province as the research object, this paper systematically analyzes the dynamic characteristics and evolution mechanism of water quantity and quality of goaf water in Shandi River Basin by using a long series of systematic monitoring of water quality and quantity, and statistical methods.

Results The results indicate that the average pH of the total outlet of "goaf water" in Shandi River is 3.58, the average TDS is 4744 mg/L, and the average SO₄^2- is 3327 mg/L. After the rise of groundwater level in rainy season, the increase of contact area or volume and the lag of rainfall are the main reasons for the nonlinear correlation between the flow of goaf water and the conductivity and SO₄^2- concentration of hydrochemical characteristic indexes. The strong oxidation reaction of pyrite in coal measure strata mainly occurs in the seasonal variation zone of groundwater level, aeration zone and surface. The certain depth of the gob ponding area of the coal mine is the reduction environment, which has the conditions for microbial treatment. After the "goaf water" flows out, the leakage recharge in the downstream carbonate section is 7247.08 m³/d, and the water quality is poor, which is an important pollution source of karst groundwater in Niangziguan Spring area.

Conclusions The regulation and storage period of "goaf water" flow to rainfall in Shandi river basin is half a year. The hydrochemical characteristic index is nonlinear related to the flow. The strong oxidation reaction of "goaf water" pyrite mainly occurs in the seasonal fluctuation zone of groundwater level, aeration zone and surface. After the "goaf water" flows out, the leakage recharge in the downstream carbonate section is 7247.08 m³/d, SO₄^2-, Fe and Mn exceed the standard seriously, which is an important pollution source of karst groundwater in Niangziguan Spring area. It is urgent to carry out the treatment of "goaf water" in coal mines and the ecological restoration of abandoned coal mines.