Abstract: Flexible waterproof layers cannot be installed in composite walls of metro stations constructed by coverexcavation reverse method, because once water leakage occurs, it not only affects the structural durability, but also increases the cost of later sealing. Therefore, waterproofing for composite wall structure is a crucial and difficult aspect in metro station engineering construction, requiring targeted research. Method: The reasons for water leakage in diaphragm walls, inner linings and other critical locations of the composite walls are analyzed. Based on Changsha Metro Line 6 Chaoyangcun Station project, multiple waterproofing techniques in composite wall comprehensive waterproof system are introduced, including retaining structure waterproofing, waterproof coating, pretreatment of leakage points, inner lining waterproofing, and preembedded grouting pipe waterproofing. New technologies and devices used in the implementation of each waterproofing technique are presented, along with corresponding safeguard measures and precautions. Result & Conclusion: During the three years of usage after the completion of Changsha Metro Line 6 Chaoyangcun Station, no water leakage occurred, indicating that the proposed composite wall comprehensive waterproof system performs well.