Abstract: According to the distribution characteristics of hydrochemical field in Yanchi-Dingbian area, as well as its geography, structure, hydrogeological background, lithofacies paleogeographical and paleohydrogeological conditions, guided by hydrogeochemical theory, the field hydrogeological survey, water sampling and testing and hydrogeochemical methods are used to analyze the formation mechanism and influencing factors of hydrochemical field. The results show that the hydrochemical fields mainly include SO₄·Cl-Na·Mg, HCO₃·SO₄-Na, HCO₃·Cl-Na·Ca and HCO₃-Ca·Na types, with obvious horizontal zoning in the north and northwest of Baiyushan watershed, and the hydrochemical field and groundwater flow direction in reverse distribution. The hydrochemical characteristics of the area are affected by the comprehensive factors, mainly paleo-depocenter and initial salt content in strata, geological structure, migmatization, groundwater movement and fossil groundwater.