Abstract: Springs and/or spring groups are primary groundwater resources for local people in towns and villages in the southwest Sichuan Province. A study of hydrogeochemical characteristics and genesis of spring water is of scientific value and realistic significance to the local people. Chemical components, oxygen and hydrogen and tritium isotopes of the springs and surface water in the catchment area of the Erwu spring of Xichang are combined to identify the hydrogeochemical characteristics and genesis of the spring water. The chemical components analyses show that the spring waters with low TDS are neutral to weak alkalinity groundwater, and are of HCO3-Ca·Mg and HCO3·SO4-Ca·Mg types. The chemical components of the surface waters are similar to those of the spring waters. The hydrogen and oxygen isotopes illustrate that the spring waters and surface waters are of meteoric origin, and there is no isotope shift of oxygen. Moreover, tritium isotopes demonstrate that the spring waters originated from meteoric waters, and experienced a long runoff time. local fault and fold structure are helpful in leading to interaction between the meteoric water and carbonate, gypsum of clastic rocks, and the cation exchange with clay minerals of Quaternary sediments subsequently occurs, which results in the major chemical constituents of Ca2+, Mg2+, HCO- 3and SO2-4 in the spring waters. In addition, some water samples with high concentrations of Na+ and SO2-4 can be interpreted by the influence of sewage and chemical fertilizers.