Abstract: The south tower foundation of Jiangyin Bridge is located at gentle high slope.The foundation rock is composed of layered sand stone & shale.It is used ineffective treatment at the top 20 meters of the foundation piles.The composition of safty monitor web and monitor position are described.The axial force respectively at tip of the piles,at bottom of the ineffective frictional area,in the rock and the outside monitor model for deformation are established.Combined with monitor data,safty of the foundation is assessed.