Dongshan karst water system is an important water source in Lancun spring region. Finding out its supplement, runoff, and drainage mechanism is of great significance to the development, utilization and protection of the water resources in this region. Based on the topography, geological structure and groundwater flow field, this system is divided into five areas, which are recharge area, strong runoff area, runoff area, conversion area and catchment area. Water samples were collected accordingly and the distribution and genesis of Sr2+ concentration and the ratio of 87Sr/86Sr in these five hydrogeological areas were analyzed. The results show that the mass concentration of Sr2+ increases gradually from the recharge area to the catchment area, and decreases in some partial areas due to the dilution of precipitation. The 87Sr/86Sr ratio in Dongshan karst groundwater shows an obvious heterogeneity, which is only related to water rock interaction, not to runoff condition. In Dongshan karst water system, the Sr2+ concentration field is highly similar to the TDS field. This water system can also be divided into Yangxinghe karst water subsystem and Wuhe karst water subsystem.