Dalian Bay Subsea Tunnel lands from the harbor basin between the pier 3 and 4 of Dalian Port. In order to provide dry working conditions for the construction of tunnel structure in the harbor basin，it is proposed to set up water stop structure around the harbor basin，and then drain the water. This working condition makes the force of wharf structure change. The wharf around the harbor basin was built by the Japanese in the 1930s and it's the object of cultural relics protection now，therefore，the stability of the wharf structure is analyzed according to this working condition. The analysis results show that the stability of the wharf structure is reduced due to the drainage construction of the harbor basin，so it is suggested to build a new temporary cofferdam outside the wharf before dewatering，which ensures the safety and stability of the wharf structure.