The modulus of deformability of rock mass is one of the most important design parameters manufacture of stone is modulus of mass rock deformability. This parameter shows the deformation of rock before the failure stage. There are many different methods for determination of modulus of rock mass deformability. one of the conventional methods for measurement of rock mass deformability modulus is radial load testing within the borehole (dilatometer). The results of this test is becames of discontinuities in the rock mass. The result of this study shows that the normal and shear deformation of discontinuities and development of tensile stresses in the wall of the borehole are as mechanism governing the deformation of rock mass. The results of deformability in the dam shows that the shear deformation found as a predominant mechanism of the left abutment mechanism of the right abutment. In continues, in order to assess of rock mass anisotropy, the modulus of rock mass deformability was calculated in all tests and it was compared with diagram of modulus change to a depth in three direction with angle 120 degree that it was drawn with rock works Software. In the end, the amount of GSI was determined for dilatometer test by using RMR 89 and then one empirical relationship was introduced for modulus of mass rock deformation by using regression analysis between modulus measured by dilatometer and GSI parameter.