Lake Qinghai is an important part of the Qinghai-Tibet Plateau. It is important to maintain the ecological security in the northeast of Qinghai-Tibet Plateau. The discharge of groundwater along the lake shore directly affects the hydrobiogeochemical process of Lake Qinghai. However, research on this issue is still inadequate. In the study, we measured and analyzed the activity of ²²³Ra and ²²⁴Ra in the lake water, river water and groundwater in Quanwan Bay of Lake Qinghai in 2014. We discussed the horizontal and vertical distribution of activity of Ra, and also estimated the residence time of Quanwan Bay water and the discharge flux of groundwater in the Buha Estuary. The activity values of ²²³Ra and ²²⁴Ra at different end elements are 0.441 dpm/100 L and 0.026 dpm/100 L, 0.22 dpm/100 L and 0.016 dpm/100 L, 0.061 dpm/100 L and 1.30 dpm/100 L, respectively. The activity of Ra from high to low was followed by groundwater, lake water and river water. In general, the activity of ²²³Ra and ²²⁴Ra in Quanwan Bay were decreased with the increase of offshore distance from 0.047 to 0.011 dpm/100 L and 1.4 to 0.2 dpm/100 L, respectively. The activity of Ra was presented wedge in the vertical of lake water. Ra activity in different directions of conservative distribution mainly affected by the suspended particle resolution. The average residence time of Quanwan Bay water was calculated by using the water retention time model, and the source and sink term of Ra in Quanwan Bay was further analyzed. The discharge flux of groundwater was 0.054-0.109 m³/(m²·d) in the Buha Estuary which was calculated by the radium isotope mass balance model.