Based on years of working experience, this paper summarized many examples of using soil geochemical data to solve fundamental geological problems, such as the lithology of underlying strata, delineating structures, stratigraphic correlation and division. The paper described the principles and application conditions of geochemistry in solving geological problems, and explained the problems as to how to use residual halos in shallow coverage areas, arid grasslands and tropical rainforest to expand the bedrock area of geological mapping, recognize and infer the lithology of underlaying strata, how to use residual halos and superimposed halos to infer concealed structure, and how to use geochemical formational halos to divide and correlate strata. The full utilization of geochemical data of the geological survey area could improve the quality of geological mapping in mineral geological survey, and help solve problems encountered in conventional geological work. The combination of geological and geochemical exploration could improve the capability of geological interpretation of geochemical anomalies.