Combined with site investigation and monitoring data of the fifth runway in Pudong airport project, this paper demonstrates the validity of surcharge preloading with prefabricated vertical drains(PVDs) in deep soft foundation treatment, and analyzes the distribution characteristics of the differential settlement for airport runway foundation across old channel after construction. The results indicate that the settlement law of the old river region is different from the law of the normal region. And the settlement and differential settlement ratio after construction can meet the specification requirement basically. But the settlement and differential settlement in old channel area increase due to the development of thicker layer of clay. Therefore, the appropriately increased overload, PVD layout depth or cryptographic layout spacing is needed according to the distribution of the thickness of compression layer.