Abstract: Corrosion building foundations caused by groundwater is a type of natural hazard developed widely and slowly. It poses the greatest threat to the foundations of towns in the red beds area. Taking the City of Tianshui, located on red beds, as an example, the author studied the causes of generation of corrosive groundwater based on long-term historical chemical analysis of groundwater data. The countermeasures of preventing building foundation from corrosion by groundwater are recommended at the end of the paper.