Mercury is important for seismic underground fluid precursory monitoring and thus is widely used in earthquake monitoring and prediction and surveying of active faults.Mercury observation techniques have been used in seismic monitoring and prediction since 1985,and since then a mercury precursory monitoring network has been established to monitor mercury in groundwater and escape gas from groundwater and soil.This has enabled the prediction of a number of earthquakes.In this study,we outline the development course of mercury monitoring,conduct a summary of mercury analysis,and determine urgent issues related to mercury monitoring.