The nonparametric method based on the maximum entropy method of random matrix was used to model the dynamics of uncertain rotor system. The effects of model uncertainties and parametric uncertainties on the fluctuation of natural frequencies of an uncertain double disk rotor system were studied with nonparametric method. The sensitivity of vibration responses of this system to model uncertainties and parametric uncertainties in different speed ranges was studied. Thus

the modeling errors that cannot be considered by parametric methods were taken into account. The results showed that: the effects of model and parametric uncertainties on system natural frequency fluctuation were different. For variation coefficient 0.04 of elastic modulus of rotating shaft

the first-order natural frequency had 1.19% and 3.58% fluctuation

and the second-order natural frequency fluctuated by 1.82% and 3.64%; for variation coefficient 0.04 of support stiffness

the first-order natural frequency had 0.01% and 6.17% fluctuations

and the second-order natural frequency fluctuated by 0.68% and 6.18%

respectively. The sensitivity of vibration responses of the rotor system to the two kinds of uncertainties was related to speed ranges: within the range of lower than 120 rad/s and upper than 430 rad/s

the system responses were not sensitive to the two kinds of uncertainties; within the range of 120-200 rad/s and 270-430 rad/s

the effects of model uncertainties on the response fluctuation were greater than those of parametric uncertainties. The research results can provide a theoretical reference for the prediction of random responses of complex rotor systems.