This paper provides a detailed introduction to the large-scale steel structure roof siphonic rainwater drainage system for airport projects in coastal areas with high-temperature,high-humidity,and high-salt mist.The forward design,calculation,and installation of pipeline routing and material selection are carried out based on regional characteristics and specifications.It also explains the overall coordination and cooperation between the siphonic rainwater drainage system and the roof steel structure and roofing design during the forward design phase.