The proposed construction site of heavy cargo wharf of Xiapu nuclear power plant in Fujian Province has an ultra-thick soft soil layer of 40~50 m.The pile-soil interaction of ultra-long friction piles used in wharf foundation is more complex than that of short piles and middle long piles,and many problems belong to the critical fuzzy range of the design code.The displacement,internal force and side friction of ultra-long piles under horizontal and vertical loads are calculated and analyzed by finite element method.The distribution trend of horizontal displacement and internal force of ultra-long friction piles in ultra-thick soft soil is summarized.For ultra-long friction piles,it is more reasonable to provide layered side friction for the same soil layer,and the side friction under 50 m mud surface will continue to increase with the depth of soil layer,and the growth rate is faster than that above 50 m.