The article deals with the modeling of stiffness properties of the rotors flange joints, which largely determine overall dynamics. Research is conducted on the example of the standard compressor shaft flange connection and the disk of the high-pressure turbine in the gas generator of the gas turbine engine (GTE). It is noted that the bending stiffness of the flange connection is a nonlinear function of the bending moment, whose both experimental and analysis magnitude is related to the rotor deflection from the unbalanced forces. It is shown that the value of the bending stiffness essentially depends not upon the flange connection geometry but on the bolts tightening force, the axial force, the tensile joint, the contact strain of the flange surfaces. Analysis of the effect obtained in different models of the flange connection of the bending stiffness values on the overall dynamics of the rotor showed the necessity of taking into account the entire set of factors acting in the joint.