A shaft-blade combined vibration model for the long blades of the low pressure turbine was presented in this paper using the method of considering the blade as a lateral vibration system with one end fixed to a shaft section. The shaft-blade combined model of the entire turbine-generator shafts for torsional vibration analysis was given by analyzing the interaction among the shaft sections during torsional vibration, and the vibration analysis response calculation method was given as well.