Abstract: The Muxing Plain is a typical plain-hill area in Northeast China, with unique hydrogeological conditions. The authors took samples of 15 groups of groundwater and 11 groups of surface water to study the chemical characteristics, formation and evolution of chemical composition of groundwater and surface water in the southern Muxing Plain, using mathematical statistics, Piper three-line diagram, ion proportion coefficient and other technical methods. The results show that the groundwater and surface water are both freshwater with low total dissolved solids (TDS). The anions are dominated by HCO₃^-, and the cations are mainly Ca²⁺ and Na⁺. The surface water is mainly composed of HCO₃^--Ca²⁺ ·Mg²⁺ and HCO₃^--Ca²⁺ ·Na⁺, and the groundwater is mainly composed of HCO₃^--Ca²⁺ ·Na⁺ and HCO₃^--Ca²⁺ ·Mg²⁺ ·Na⁺. The hydrochemical characteristics of surface water and groundwater are jointly controlled by water-rock interaction, cation exchange and adsorption and mineral activities. The water-rock interaction is mainly silicate dissolving action, and mineral activities has an extensive-scale influence on surface water and large-degree influence on partial groundwater. The results could provide theoretical support and scientific basis for the utilization and protection of water resources in the southern Muxing Plain.