Abstract: There are two kinds of underground water circle dynamic types of Beijing City east main canal of South-to-North Water Diversion Project: penetration, evaporation, runoff type and penetration, runoff type. This two types all absorb atmosphere rainfall to support runoff. The dewatering modes are underwater cross runoff and overflow, the whole flow direction is from northwest to southeast. Distribution of bed rock crevice water and loosen pore water in this region are controlled by structure. The underwater circle law is researched to reduce the hazard of geology changes to pipelines.