Apply digital image processing technique of the triaxial test soil deformation to the study of stress-stain characteristics based on local deformation measurement of soil specimen. Compared with the results of tranditional whole deformation measurement, the influences of end restraint and end contact on strain-stress characteristics are determined quantitatively. Select the nonlinear-elasticity model along with elastoplastic model to study the stress-stain characteristics of typical soils. Based on the the test data and characteristics of constitutive model, the models and their parameters determination methods are improved to refect the stress-stain characteristics of soils more accurately. Use the test data from local deformation measerment and traditional measerment to analyse the influences of the variation poisson��s ratio on results and to study the experiment method and value determination method of poisson��s ratio. Start from the elastoplastic model, the deformation characteristics of sandy material in cyclic loading are investigated, the influences of partical breakage on stress-strain characteristics of sand are analyzed, and the law of expansion in loading and contraction in unloading is quantitative analyzed.