Abstract: In order to make clear the water-filling source of Hulusu coal mine during water inrush of poorly sealed gas hole, some evaluation methods(e.g., piper three wire drawing, hierarchical clustering law) were used to analysis the hydrogeochemical characteristics of water samples. The results showed that the concentration of TDS decreased gradually. During Initial stage of water inrush, water was of SO₄·Cl—Na type and located at the right end of piper three wire drawing and came from Zhiluo Formation. During the middle stage of water inrush, the concentration of TDS decreased to about 500 mg/L. The sampling points were located at the lower right end of piper three wire drawing, water was of HCO₃·SO₄·Cl—Na type and came from Cretaceous System. During water inrush, water of SO₄·Cl—Na type with high TDS gushed out from seam bottom, the water sampling points, the sampling points were located at the upper right end of piper three wire drawing. During treatment of gas hole, γ(Ca)/γ(Na) coefficient in the water was much higher than that of other water samples, and HCO₃^- was not detected, the water had hydrochemical characteristics of Zhiluo Formation water in seam roof, showing that the hydraulic connection between seam 2^-1 and Cretaceous aquifer and seams 2-6 aquifers was cut off. Taking 20 as distance threshold value, hierarchical clustering analysis could divide the water samples into Cretaceous water and Jurassic water, and the distance threshold 5 may divide further the water of Jurassic aquifer into water of second member and first member of Zhiluo Formation, water of seams 2-6 aquifers, realizing accurate discrimination of the variation law of water-filling source during water inrush of gas hole.