On the basis of series of indoor tests for unsaturated Nanning expansive soils，non-liner rheological characteristics of the expansive soils have been studied. The results showed that the strain-time curves have the same trend under loading，step-loading and preloading，while the soil showed linear deformation under small stress，and the strain-time curves can be fitted in logarithm form under large stresses. Through the experiment, creep curve can be composed of Bu model and equation of constitution and the creep of the expansive soils also can be obtained.