Determination of geomechanical properties of rock massif presents difficulties due to the problems arising in sampling, specimen preparation and testing. Questionable is also the accuracy of the results for more complex formations since the tests are usually conducted on small specimens that cannot depict the structure. One of the methods used to directly evaluate the actual geomechanical properties of the rock mass is a dilatometer analysis. The improvement of the standard dilatometer back analysis has been done recently by Kuklík and Záleský (2008). The newly developed formula presents new boundary condition and also incorporates the thickness of plastic zone layer as a new parameter. The aim of the presented work is to focus on numerical back analysis of standard dilatometer test using FEM and verify the accepted assumptions of the new formula numerically.