To analyze the rotor vibration characteristics induced by partial admission in the control stage of a steam turbine, computational fluid dynamics methods were used to study the time-frequency spectral characteristics of rotor aerodynamic excitation forces under various load conditions (100%, 75%, 50%). Concentrated aerodynamic forces were applied to the rotor, and the effects of these forces on rotor vibration response characteristics were investigated using modal analysis and transient dynamic analysis based on finite element methods. The results reveal that in the X direction, load conditions significantly influence the vibration displacement of the rotor system. The peak response frequency of the control stage disk in the X direction is 405.40 Hz, while the peak frequency at the rotor centroid is 38.61 Hz. Under symmetric admission conditions, the acceleration response of the rotor system remains relatively stable with load variations. In contrast, under asymmetric admission conditions, the rotor acceleration exhibits significant fluctuations in the X and Z directions. The displacement peak at the bearing is smaller than at the rotor centroid and the disk edge. The rotor shaft primarily exhibits bending vibrations, while the disk is dominated by torsional vibration modes.