With its important geographical location and status as the largest saltwater body in China, Qinghai Lake plays a vital role in the ecological environment of the northeastern part of the Qinghai-Tibet Plateau. Due to climate change and the subsequent adjustment of Qinghai Lake’s tourism policy, it is necessary to understand groundwater discharges in southeast of Qinghai lake both for ecological protection and risk prevention. This study used radium isotopes ²²³Ra and ²²⁴Ra to trace groundwater discharges and nutrients carried into the lake. The spatial characteristics of Ra isotopes with greater activity in the upper and bottom layers in the lake indicated that they were influenced by inputs of shallow groundwater and diffusion from sediments. The average ²²⁴Ra diffusion flux of the sediments in the Lake was 33.54 dpm m⁻² d⁻¹. Based on the ²²⁴Ra mass balance model, the discharge flux of shallow groundwater in this region was estimated to be 3.49 × 10⁶ ∼ 3.68 × 10⁶ m³ d⁻¹. The PO₄³⁻ and SiO₂ fluxes carried into the southeastern of the lake by groundwater were 1.78 × 10¹¹ ∼ 1.88 × 10¹¹ mg/y and 2.22 × 10¹² ∼ 2.34 × 10¹² mg/y, respectively. It is thus essential to monitor shallow groundwater discharge into Qinghai Lake for the protection of the water environment and prevention of potential ecological risks.