Based on the mass conservation law and the method of chemical thermodynamic equilibrium constant, a mathematical model for calculating the existing forms of groundwater chemical components and its mass concentration was established. Based on MATLAB, a corresponding program to calculate the groundwater quality testing data of Chaoyang District, Beijing was written. The results show that the existing forms of groundwater chemical components include single ions, complex anions, complex ions and complex molecules; Dissociative Ca2+, Mg2+, SO42-accounted for mass concentration of Ca2+, Mg2+, SO42-, respectively, 8526％,8701％,6985％, which claims the difference between analysis concentration and calculated concentration; The value of pH exerts an influence on the concentration of free ions in groundwater, which causes the changes of ion migration ability.