Abstract: For about a decade, variations in hydrogeochemical constituents have been used for earthquake prediction in China. The experiences in foretelling several earthquakes have indicated that hydrogeochemistry may be an possible means for mid and short-termearthquake predictions. In this paper, by outlining the characteristics of hydrogeochemical anomalies observed before several strong earthquakes with M7 occurred in recent years in China, particularly three of them occurred in North China, an attempt is made to discuss the role of hydrogeochemistry in earthquake prediction and the main factors that influence precursory variations in hydrogeochemistry. Furthermore a preliminary study on the mechanism of the precursory hydrogeochemical anomalies is made.