Abstract: In this paper, the elastoplastic constitutive relationship of soils which is de rived from the normality between the yield surface and the direction of plastic strain increments is simply discussed. The methods to determine elastic compressive bulk modulus, K, elastic shear modulus, G, hardening parameter, H and yield function, f, by using experimental data are described, Finally, the comparison is made between the calculated results from substituting those parameters into incremental elastoplastic stress-strain relationship for several kinds of stress-path and the test results.