Abstract: Base on the displacement back analysis and in accordance with the special characteristics of structural planes in rock masses, the weighted displacement back analysis is introduced to determine the parameters of possible stable control planes using in site measured displacements. Then the validity of weighted displacement back analysis is proved through sensitivity analysis. As an example, the parameters c,f of some siltized intercalation in a rock slope of a practical project are obtained by the use of this method. The results show that this method has high practical value.