Abstract: Mercury is one of the sensitive constituents in subsurface fluid for earthquake moni-toring and prediction. Authors analyzed interference factors in the process of mercury ob-servation in groundwater, and pointed out that distilled water, chemical reagents, temper-ature and adsorption mainly cause the variation of background data. Finally, the methods for elimination of contamination and identity of anomalies are presented.

Key words: Mercury observation, Interference factors, Elimination contamination