Abstract: In the study of the hydrogeochemical background, it has been found that the enrichment of the dis-solved CO₂, H₂ and He in groundwater in Hebei Province can be related to the seismically active belts,deep fault zones and the upper crust boundary, and their relationships are discussed in detail.Based on the characteristic distribution of CO₂ and δC13 analysis, it has been suggested that the CO₂ enriched in those zones mainly originated from the metamorphic reactions in carbonate rocks; H₂ and He may derive from igneous rocks in the upper crust according to their distribution and possible genetic mechanism.Therefore, CO₂, H₂ and He are probably the important hydrogeochemical component to indicate the po-tential focal zone and monitor the earthquake activities.