Research conclusions:(1)Caohai engineering geology condition of Dianchi lake is complex，the main engineering geological problems are peat soil，regional major fault and earthquake，the area with high seismic intensity of sand lIIIuefaction and soft soil subsidence，the shallow natural gas and so on .They have a large influence on engineering. (2)The engineering through Caohai can use tunnel and bridge scheme，the tunnel scheme is better by comprehensive comparison. Tunnel construction can use two process of cut and cover method and shield tunneling method，cut and cover method can use two kind of construction methods of cofferdam cut and build island cut，shield tunneling method has minimum impact to natural ecological environmental. (3)The geological conditions of Caohai and Dianchi lake area are similar, have the same engineering geological problem. The road engineering through the Dianchi lake should use shield tunnel scheme. (4)The research results can provide references for underground engineering of soft soil area.