In order to study the dimensional influence of tunneling on adjacent pile foundation, successive segmental excavation is simulated considering the geological background in Nanning. The different stiffness ratio of pile and soil is obtained by changing the pile’s elastic modulus, radius or length. The additional displacement and inner force due to tunneling are compared for different stiffness ratio. Many useful conclusions can be drawn. Foundation settlement occurs on the top of the tunnel while upheaval arises below the tunnel. The range of influence is enlarged with the distance from tunnel. Pile foundation is influenced obviously in the area of 1.5 times tunnel diameter from the tunnel face. The additional displacement changes clearly with different stiffness ratio, especially the vertical settlement. The conclusions will be useful for the construction and design of tunnel.