Abstract：In order to study the influence of principal stress axis cyclic rotation at low shear stress level on clay¢s behavior，a series of experiments of Hangzhou typical intact soft clay were conducted. The experimental results reveal that the stress paths such as principal stress axis cyclic rotation with constant shear stress lower than the limit shear stress bring the variation of samples¢ strain components and pore water pressure into dynamic equilibrium；the stable values of equivalent stiffness and pore water pressure at equilibrium are mainly decided by the tortional shear stress component；and the axial stress component also promotes these two values when the tortional shear stress components are the same. Meanwhile，such principal stress axis cyclic rotation causes the stiffness to be enhanced during the following static shear stage. Especially，when the following stage is triaxial compression one，the strength will arrive in advance observably，and the directions of principal stress increment and principal strain increment become obviously non-coaxial at the initial of triaxial compression，which are mainly caused by the residual strain and changes of soils¢ structure generated in the previous cyclic principal stress axis cyclic rotation. But the static shear strength and critical pore water pressure in the following static shear stages are not greatly influenced by the previous principal stress axis cyclic rotation.
