Abstract: Accurate prediction or detection of Karst and groundwater is a difficult problem to be solved. It is great significant to study the mechanism of Karst and groundwater action for the problem solving. Further study on the hydro-chemical characteristics of Karst groundwater will help to better understand the runoff circulation conditions and geological environment. Based on the simplified hydro-geochemical model of Karst groundwater, the chemical composition of Karst tunnels and the hydrochemical kinetic parameters of Karst groundwater are analysized. On this basis, Ions of conventional hydro-chemical constituents are paired by borrowing the theory of complex reaction in analytical chemistry, the proportion relation of each ion pair are explored by changing the observation scales, self-similarity and scale invariance of the cumulative fraction of ion pairs are demonstrated. Thus the feasibility of applying fractal theory to study the chemical characteristics of Karst groundwater is proposed.