As a fragile factor of karst ecosystem, karst underground water system is highly sensitive to landuse change. Taking Houzhai subterranean stream basin, Puding County, Guizhou Province as an example. The im- pacts of intensity of agriculture activities, landuse change and irrigation system change upon underground water were analyzed based on more than 20 years' hydrochemical data. The results showed that both intensification of a- griculture activities, landuse change and irrigation system change can bring spatial and temporal change of under- ground water quality. Some are beneficial, such as co-irrigation of ground and underground reservoirs, vegetation planting(from farmland to forest); others are disbeneficial, such as urbanization, direct discharge of waste, and overuse of pesticide and fertilizer. Accordingly, underground water vulnerability should be considered during the landuse planning, thus help the harmonious development between human activities and resources and environ- ment.