The groundwater flow system is a groundwater system with a unified spatio-temporal evolution process consisting of a source group from source to sink. The concept of groundwater flow system is based on the understanding of groundwater seepage field, in addition to the spatial differences in hydrogeological parameters, do not deliberately distinguish between aquifers and aquifers. It is the basic unit of groundwater resources evaluation by the boundary geological limit and the water geological body with unified hydraulic connection. Groundwater base units with water, water input, transport and output, and combinations thereof.