The existence of shallow gas seriously affects the stability of seabed formations. In the early stage of the construction of the Jiayong Cross-sea High-speed Railway Bridge, during the preliminary survey of the west line of Haiyan, the central sea area of the bridge frequently encountered shallow gas. On the basis of exploration, physicochemical test analysis, etc., the hydrogeological conditions, stratigraphic deposition, and shallow gas distribution and origin of the shallow gas-rich area at the bridge site are discussed, and the possible shallow gas disasters and genesis of the bridge construction at various stages are analyzed. corresponding preventive measures. The research shows that the formation water in this area is mainly Quaternary loose rock pore water, and the gas-bearing soil layer is Quaternary Holocene to Lower Pleistocene alluvial clay and sandy soil, of which the sandy soil layer is the main gas storage layer. The gas belongs to the typical primary type early biogenic gas that is not affecte