Abstract: A rotor-blade model was established for analysis of the coupled shaft torsional vibration and blade bending vibration, which was used to analyze the last stage long blades in a 600 MW turbo-generator set. Based on the model, the method combining Riccati transfer matrix algorithm with Newmark-β method was used to obtain the displacement response curve of blades when shaft torsional vibration happens. Through Ansys calculation, the displacement-stress curve of blade was acquired, while the dangerous section of blade was determined, together with the stress history obtained, which may serve as a reference for online fatigue life analysis and safety assessment of the rotor and blade.