Abstract: In order to illustrate the hydrochemical evolution law of groundwater in the concealed coal mines in North China, taking the Renlou mine in Huaibei coal field for example, hierarchical cluster analysis and principal component analysis are used to analyze the conventional hydrochemical data (K⁺+Na⁺, Mg²⁺, Ca²⁺, Cl^-, SO₄^2-, HCO₃^- and CO₃^2-) of the fourth aquifer of the Quaternary, the coal measures, Taiyuan Formation limestone and Ordovician limestone. Based on these analysis, different hydrochemical types are partitioned and hydrochemical formation conditions are clarified accordingly. Research results show that "desulfurizing" suggests increasing closeness in the groundwater system and decreasing mining disturbance while "hardening" suggests decreasing closeness in the groundwater system and increasing mining disturbance, and "salinizing" lies in "desulfurizing" and "hardening" process. Because of mining disturbance and "salinizing", "desulfurizing" and "hardening" show almost opposite trends in the groundwater system.