The foundation of the gravity anchorage is usually simplified as shallow foundation, which is diseconomy when the depth effect is neglected. Because the embedded depth of caisson foundation south anchorage of Taizhou Bridge is 42 m, FEM(finite element method) is utilized to research the depth effect of the caisson foundation in the stability computing. It is clear that the depth effect improves the bearing capacity of anchorage foundation dramatically by comparing the variation of the displacement and the rotation angle of the anchorage foundation in the periods of construction and operation.