Abstract: A self- oscillation characteristics model and a dynamic response model of large hydro- electric genarating set considering all kinds of affecting factors are established. Based on finite element method, the calculating formulas of the critical speed and the dynamic response are developed, the programs that fit to the large software are compiled, and an engineering example is calculated and analysed. The influence and influence degree of various factors such as gyroscopic effect, electric- magnetic forces, stiffness and damp to vibration properties are discussed. The results indicate: the gyroscopic effect and stiffness have obvious effect on critical speed, the electric- magnetic forces cause little effect to self- oscillation characteristics and these forces are main loads for dynamic displacement. The calculation model and the calculated results are rational ,and afford some theory supporting for the vibration design and the research of vibration reduction of large hydro- electric generating set.