Abstract: In recent years, submarine groundwater discharge (SGD) has been recognized as an important process in land-ocean interactions in the coastal zone (LOICZ). The subject has thus become the focus of intensive research. Geochemical tracers can be effective tools for estimating SGD in LOICZ. The objective of this study is to estimate SGD in the Wuyuan Bay using Radon-222 (²²²Rn) as naturally occurring tracer. The dynamic variation of SGD can thus be subsequently assessed. We continuously measure the seawater ²²²Rn and ²²⁶Ra activities, the near-sea surface air ²²²Rn, wind speed, sea water temperature and depth for two consecutive days. We also deploy an incubation device to measure the diffusive flux of ²²²Rn from sediments and the pore-water ²²²Rn activities. Based on the mass balance principle for the ²²²Rn flux, the measured seawater ²²²Rn are corrected for the decay product of parent ²²⁶Ra, the effects of tides, the losses to the atmosphere, the diffusive influxes from the sediments, and the mixing with offshore seawaters. The result shows a conservative estimate of ²²²Rn flux attributed to SGD is between 0 and 126.7 Bq/(m² h), which can account for 54% ²²²Rn in seawater. Taking a SGD end-member as example, the calculated SGD input rates range from 0 to 29.3 cm/d with an average value of 9.3 cm/d. The end-member is made of the weighted average of groundwater and pore-water ²²²Rn activities. The fluctuation in the SGD input rate has a 12-h period, which matches well with the semi-diurnal tides in this region. The SGD input to the Wuyuan Bay could be as much as 1.86×10⁵ m³/d if the estimation were made under the assumption that the average SGD input rate is applicable to the entire bay area. The input of terrestrially derived fresh groundwater in the Wuyuan Bay could be approximately 1.86×10⁴ m³/d if the fresh groundwater were 10% of the total SGD input.