The purpose of the present paper is to depict the clay behaviour under long-term cyclic shear conditions. The empirical relations of time-dependent shear deformation and cyclically induced pore pressure were formulated through the undrained cyclic triaxial test on plastic clay. An analytical model was presented by combination of the equation of induced pore pressure with the Terzaghi's type of consolidation theory. The model successfully explained the behaviour of generation and dissipation of pore pressure and volumetric change in clay during cyclic loading. It was suggested that the proposed model should be a clue to to predict the deformation, settlement and stability of soft clay under long-term cyclic loading with inclusion of drainage.