Investigating the surface water-groundwater interactions is of considerable significance for guiding the ecological construction and protection of the Qinghai Lake National Park. This study investigated the hydrochemistry, stable isotopes (δD and δ18O) and radioisotopes (222Rn) to identify the surface water-groundwater interactions. The results show that the hydrochemistry of river water and groundwater were mainly affected by water-rock interaction, while the pore water and lake water were mainly affected by evaporation crystallization. The hydrogen and oxygen have spatial variability during surface water-groundwater interaction along the drainage basin. The 222Rn activities of groundwater and river water were higher in the middle reaches than in upstream and downstream. The 222Rn activities of pore water decreases with the increasing offshore distance and depth. 222Rn activities of lake water and river water over the monitoring period shows a typical diel cycle, much higher at daytime and lower in the nighttime, indicating that groundwater discharged to river during dry seasons, and upper and middle stream and downstream accounted for 96% and 87%, respectively. This phenomenon occurred before precipitation. But there has been a shift in precipitation, that is river water discharged to groundwater, and accounted for 98%. This study contributes to useful reference of saline lake in worldwide.