On the basis of the analysis of GOST 31320-2006 (ISO 11342:1998) it is shown that existing criteria of rotor balancing quality based on residual vibration levels of pedestals (or rotating shafts vibration) or based on residual modal unbalance criteria does not provide necessary vibration reliability of turbines. It is suggested a new method of estimate flexible rotors balancing quality based on pedestal dynamic forces levels. It is shown that the modal balancing of flexible rotors and suggested criteria of estimate flexible rotors balancing quality allow to compare balancing quality of resemble rotors and lay the foundation of equal quality rationing of different rotors balancing.