Abstract: The present disclosure relates to analysis of Hg(II) isotopes in the aqueous phase, and provides an in-situ enrichment method and an analytical method for Hg(II) isotopes in the aqueous phase. The in-situ enrichment method includes the following steps: conducting adsorption in the water sample by a diffusive gradient in thin-films (DGT) device to obtain an Hg(II)-adsorbed DGT device; where a binding gel of the DGT device is an NSBA gel; conducting elution on the NSBA gel in the Hg(II)-adsorbed DGT device to acquire an Hg(II)-containing eluate with a mercury concentration higher than or equal to 0.5 ng/mL; where the elution is carried out with an eluent of reverse aqua regia. In the in-situ enrichment method, the NSBA-DGT device only needs to be placed in the water sample to be investigated to perform in-situ Hg(II) adsorption without direct grab sampling.