Based on the numerical modeling constitutive law of rock and soil

the stress-strain relations of expansive soil of the Linhuaigang Dam in Anhui Province with different water content were established; and the three dimensional surface of stress-strain relation in the whole stress field （p

q） were drawn through visualization. By comparison

it is found that the effect of different water content on the constitutive relation of expansive soil is obvious. The theory of plastic potential is not used in this paper

in the numerical modeling not only the difficult of seeking analytical expression of plastic potential is overcome

but also the initial condition

such as water content can be chosen freely. Therefore

the deformation of expansive soil could be really described by using the constitutive model provided by the numerical modeling.