Abstract: The study on geotechnical backanalysis has long been recogonized as an important subject in the safty analysis of the underground structure construction. Sensitivity analysis for displacements against elasto plastic parameters takes a crucial role in the study.In this paper, the Drucker Prager constitutive model is used to simulate the nonlinear mechanical behavior of soils. With introduction of the natural coordinates into the stress space, the hydrostatic and deviatoric stresses are separated each other and the sensitivity formulations are then derived in a close form.