Abstract: There are abnormal geological structures like karst caves and underground rivers in the contact area be? tween the insoluble rocks (such as sandstone and mudstone) and soluble rocks(such as carbonate rocks) in the red bed area of central Yunnan Province. Taking the Shanchongqing tunnel on Yiliang-Shilin expressway for example,the hydrogeological conditions of the underground river in the typical interspersed contact zone is analyzed by means of geological interpretation, investigation of water outlet at ground surface, apparent resistivity detection with transient electromagnetic method and geological radar scanning inside tunnel. It concludes that the water supply of the karst river is ground surface fissure water without regional connection, and tunnel water inflow is predicted as well as basic treatment methods are proposed.