Climate change has intensified extreme rainfall events and increased urban pluvial flooding risks, revealing the inadequacies of traditional drainage infrastructure. Deep tunnel sewer system (DTSS), as a kind of strategic resilient infrastructure, offers an important engineering pathway for enhancing drainage and flood−control capacity in high−density built−up areas of megacities and large cities through rapid conveyance, large−scale storage, peak attenuation, and environmental improvement. International practices indicate that deep tunnels can alleviate shallow drainage network bottlenecks under suitable hydrological, hydraulic, and operational conditions, while generating co−benefits in overflow pollution control, water environment improvement, and intensive land use. Domestic practices in Guangzhou, Shanghai, Wuhan, and other cities further demonstrate the potential of DTSS. Over a review of existing practices, this article analyzes the mechanisms and comprehensive benefits of DTSS, and identifies main issues in planning, construction, and operations of DTSS. It is argued that although DTSS cannot universally replace conventional drainage facilities, they serve as a strategic infrastructure backbone for urban areas featuring high density, intensified flood risk and substantial asset exposure to flood. Policy recommendations are proposed in terms of watershed−scale planning and design, investment and financing mechanisms, as well as construction and operation standards.