Abstract: Stress change of pile-soil interface for jacked-in piles during pile-sinking in clay is a topic of concern in the geotechnical engineering. A full-scale jacked-in pile is penetrated into the clay in Dongying city of China and studied by monitoring the laws of the excess pore water pressure and soil pressure of pile-soil interface with depth at different pile locations of h/L. The relationship between the excess pore water pressure of pile-soil interface and the effective pressure of superimposed soil at different pile locations of h/L and the characteristics of soil pressure of pile-soil interface at the same penetration depth are analyzed. Especially the causes to influence the distribution of the effective soil pressure of pile-soil interface are studied. The test results show that the maximum ratio of the excess pore water pressure of pile-soil interface to the effective pressure of superimposed soil during pile-sinking is 1.08 at different pile locations of h/L and decreases gradually along the pile from pile tip to pile top. The soil pressure of pile-soil interface presents “lateral pressure degradation” with the relative depth of the increasing pile tip（h/L）at the same penetration depth. The “lateral pressure degradation” presents obviously with the relative depth of the increasing pile tip（h/L）. The effective soil pressure of pile-soil interface is only 10 kPa at the location of h/L=11/12, and that of certain interface at other different pile locations of h/L is 1.88~2.20 times the excess pore water pressure of pile-soil interface. The proposed solution is of great engineering significance for jacked pile construction and bearing capacity design in clayey foundation.