Abstract: A new means of deformation measurement is introduced for unsaturated soil specimen in suction- controlled isotropic compression tests based on the digital image measurement method. The deformation of the whole unsaturated specimen and the middle section that is relatively little influenced by the end restraint can be measured by this method. Results of suction-controlled unsaturated compacted soil isotropic compression tests show that the v-p and v-lnp curves of the middle section are evidently different, that the LC locus of two kinds of model parameters are also different, and that the elastic range based on the whole specimen deformation is bigger than that on the middle section in both tests and model prediction.