The paper deals with the application of the cavity expansion theory for the determination of soil strengths and non linear deformation parameters using pressuremeter tests. The developed cavity expansion theory takes into consideration the facts that even the initial soil stress-strain state itself is anisotropic, and that due to expansion soil density increases. The deformation modulus is not in a linear correlation with the soil pressure. By having introduced the deformation modulus, we have introduced two soil constants; (E_O) that is the basic deformation modulus, and (a): an exponent. The basic value of the deformation modulus depends first of all on the initial density of the soil, and the exponent value “a” is in very close correlation with the angle of friction of the soil. The soil strength parameters, namely cohesion (c) and angle of friction (φ), as well as the deformation parameters represent the soil properties. We can determine the combination of the interrelated and suitable soil parameters from the pressuremeter test. The paper presents an example, and proves that the measured diagram very well approximates the theoretically calculated diagrams with different cohesion - basic deformation modulus combinations.