The invention belongs to the technical field of monitoring of 
torsional vibration of a 
turbine-generator shaft 
system, and particularly relates to a method and 
system for monitoring large disturbance transient 
impact torsional vibration of the 
turbine-generator shaft 
system. The method comprises the steps of carrying out 
simulation calculation on shaft system 
torsional vibration caused by large disturbance of a power system under the coordination effect of an electromechanical network, establishing the correspondence between the maximum value of the 
electromagnetic torque of a generator and the fatigue life loss of the shaft system under large disturbance of the power system, setting a damage alarm threshold value and a 
tripping halt protection threshold value, calculating the 
electromagnetic torque of the generator according to the three-phase current and 
voltage of the generator, sending a damage 
alarm signal or a 
tripping halt protection 
signal in time when the safety of a generator set is threatened, and finally carrying out shaft system torsional vibration dynamic response calculation on the torsional vibration fault so as to accurately estimate the damage degree and the 
remaining life of the shaft system. By means of the method, on-line monitoring, analysis and protection of torsional vibration caused by the large disturbance fault of the power system be achieved, and accurate calculation of the fatigue life loss caused by torsional vibration of the 
turbine-generator shaft system can be achieved at the same.