In order to study the vibration reliability of hydraulic turbine-generator unit, the nonlinear dynamic equation of the main shaft system of hydraulic turbine-generator unit is established by the finite element method. Then the nonlinear vibration characteristics of the system are analyzed and the excitation frequencies of the system are obtained by the method of multiple scales. Based on the criterion that the absolute values of difference between the natural frequencies and excitation frequencies of the system should be less than specific values, the hybrid probabilistic, nonprobabilistic, and fuzzy reliability model of the system based on nonlinear vibration is constructed. By the hybrid reliability model, the reliability of system can be calculated. Finally, an example is presented.