In tile paper, a visco elastic-plastic constilutivc model and a method for determining model parameters for soft clay are presented. In this model tOlal strain of soft clay is assumed to be divided into three parts: instantaneous elastic, visco-elastic and visco-plastic. The characteristics of instantaneous and visco-elastic deformation of soft clay are simulated by Merchant's model, the plastic is by a model with two yield surfaces. And related conslilutive equatiorn is conducted. A number of slress-controlled triaxial tests are pertormed to calculated tile model parameters. The visco-elasto-plaslic model is used lor analysis of the displacement of an embankmenl on soft groud dy use of three-dimensional finite element method. Tile predicted settlements agree well with tile measured data. It is indicaled thai the viscous characteristics should be taken into account in deformalion analysis for soft elay.