Abstract: In order to make clear the relationship between coal mining and surface runoff reduction in Balasu Coal Mine, based on the analysis of hydrogeological conditions in the project investigation and evaluation area, the GMS underground water numerical simulation software was used to establish the underground water numerical model in the evaluation area, quantitative analysis and evaluation of the attenuation change curve of main surface runoff that change with the underground runoff recharge from coal mining. The results show that the attenuation rate of underground water spillover is less than 12.00% in all valleys, and after 49 years of coal mining, the attenuation of surface runoff increases obviously. The main factors are surface subsidence caused by coal mining, and the rise of quaternary phreatic water level, which causes the invalid evaporation to increase, thereby, the amount of water supplied to the surface runoff is reduced.