Expanded poly-styrene(EPS) is a new material to reduce the subsidence of the bridgehead of soft embankment. Traditional design and material selection of EPS embankment does not take into account the basic characteristics of creep. Creep tests of EPS specimens in varied density and pressure are performed. Results are as follows:Uniaxial compressive strength and anti-deformation ability of EPS linearly rise up with increasing density; creep deformation of EPS depends on the stress factor. Creep deformation increases closely linearly with the stress factor and becomes stable fast when the factor is less than 0.6. However the creep deformation increases nonlinearly and rapidly and becomes unstable when the factor is more than 0.6. Conclusion from the creep test can determine the design value of compressive strength of EPS and the corresponding density requirements. The relation between the creep deformation and time follows the hyperbolic curve, and the corresponding constitutive creep relation is presented. The method to obtain the parameters is introduced. Case studies show that the constitutive relation of EPS presented better reflects the creep behaviors of EPS.