In order to understand Lacustrine Groundwater Discharge (LGD) in the Da Qaidamsalt lake, the radium isotopes activity value of brine, deep hydrothermal groundwater, shallow groundwater water, and river water were measured. The results showed that the activity value of 223 Ra, 224 Ra, 226 Ra and 228 Ra of lake water increase with increasing salinity, followed by a decrease when salinity exceeds 168. 99‰, suggesting that radium was desorbed when groundwater or river water met salt lake water at beginning, and radium was co- precipitated at a later stage in salt lake evolution. The activity value of 223 Ra, 224 Ra and 228 Ra in deep hydrothermal groundwater are higher than that in the natural outcrop hydrothermal groundwater. However, 226 Ra activity shows antipodalvalues, and there is an obvious accumulation phenomenon in the surface hydrothermal groundwater. The fraction of deep hydrothermal groundwater, shallow groundwater and river water are 0. 01, 0. 31 and 0. 68, respectively. The radium apparent ages ranged from 2. 24 to 18. 65 d with an average 9. 13 d in the lake water. LGD was estimated with radium inventory model, leading to a deep LGD and shallow LGD estimate of 1. 24×103± 12. 20 m3/d and 2. 09×106±3. 20×104 m3/d, respectively. This work provides an effective method for evaluating lacustrine groundwater discharge in a salt lake.