The wastewater drainage system is an important part of the underwater traffic tunnel constructed by mining method. The drainage capacity determination of wastewater drainage system, wastewater lifting scheme and optimization design of wastewater pump room of Qingdao Jiaozhou Bay Subsea Tunnel are analyzed; and the key technologies of wastewater drainage system of subsea tunnel constructed by mining method are discussed. Some conclusions are drawn as follows: (1) The key to the determination of the wastewater drainage capacity lies on quantitation of tunnel structure water leakage; and the conventional quantitation of underwater tunnel structure water leakage cannot be taken as reference for subsea tunnel. (2) The wastewater lifting scheme is closely related to economy and safety; and the core is the wastewater pump type selection. (3) The wastewater pump room can be optimized from the aspects of wastewater tank volume, structure design, equipment maintenance, etc. (4) The drainage system of subsea tunnel constructed by mining method should be determined according to the actual construction conditions to realize safe and economic design.