To improve the service quality of underwater highway tunnels and ensure the safety of tunnel traffic, it is urgent to establish an inspection and assessment system and solve the problems such as multiple risk points of civil structure, frequent failure of mechanical and electrical facilities, and hard implement of preventive maintenance and maintenance decisions. It is of great significance to carry out quality upgrading of underwater tunnels. Relying on Yangcheng west lake tunnel in Suzhou, China, the quality upgrading schemes for improving performance of the facilities, information level of management and maintenance, and safety risk prevention and control are systematically proposed. Main works conducted are as follows: (1) Disease treatment of structures, renovation and upgrade of facilities, and implementation of performance improvement of traffic safety facilities. (2) Establishment of an informatization system for tunnel management and maintenance. (3) Establishment of a tunnel inspection and assessment system and a risk identification and prevention system for operation period. After the implementation of the quality upgrade program, the technical conditions, information maintenance level, and risk prevention and control ability of Yangcheng west lake tunnel have been improved remarkably.