The characteristics and potential risks of soft soil layers in the Bay Area are discussed in detail, and the importance of treating soft soil foundations and the basic principles to be followed are revealed. Combined with the specific engineering examples, the effective treatment methods of thick soft soil subgrade constructed at the same time with the river are studied. Two methods of bank protection+subgrade treatment are proposed combined with the urgency, economy and design requirements of the project, which are the lateral constraint support for river (precast concrete sheet piles) + light foam concrete for subgrade, and the shallow buried support (plain concrete wall + pine pile) for riverbank protection and the composite foundation (cement mixing pile) for roadbed. The overall stability of two combination methods is quantitatively evaluated and the settlement after completion is calculated (for the road center line), and these theories are applied to the practical engineering operations. The practical economy of this scheme is fully played, which provides the practical and effective reference for the road construction of the Bay Area Industrial Park with dense river networks.