Abstract: he optimal estimation of parameters in geotechnical back analysis depends upon the form ofobjective function which reflects the relation of system response of real geotechnique engineering andsimulating model.For the adverse circumstances in field testing site and the complexity of geologicalcondition,the measured displacement data are dispersed far from the assumed error distribution,suchthat previous estimator will be of no effect,A general objective function called as robust objective func-tion is presented according to Bhattacharya information inequality,the proposed approach would makefull use of measurements to get reasonably satisfactory result.