Nowadays, civil engineering makes high demands on numeral modelling in geotechnical engineering, notably, to ensure reliability of a structure at minimum cost. Using of codes and standards supported with numerical calculations and soil constitutive models makes the design satisfying this requirement possible. But no matter how complex the model is its fidelity depends on input data. The article describes a method for determining the main characteristics of the Hardening Soil model (including calculating the power parameter m and reducing the deformation characteristics of the soil to the recommended value of the reference pressure). A comparison of two approaches was made: using a table of physical and mechanical characteristics; and the approach based on the analysis of the results of laboratory tests in accordance with the methodology given in the article and further verification of the obtained parameters. The result of the comparison was the complete inconsistency of the first approach for assigning the parameters of the nonlinear soil model and the need to refer to the test protocols was confirmed.