Abstract: Unloading engineering is often met as a matter of fact,and the path of keep major stress-strain invariant and minor stress-strain reduced exist indeed in all the sress pathes.A series of experimental researches on the deformation character were made about typical clay in Wuhan and on the base of analysis of a great number of experiments the study were made on the relation of stress-strain、 volume strain-axle strain and parameter of reflecting deformation of side.This study improve the pratical deformation theory of saturated clay appropriate for the P-decreasing path and lay the foundations of seeking practice of excavation study.