Oil whip and resonance are the common faults of a rotor system. The faults directly affect its normal operation and can cause serious accidents. Based on the regularity of oil whip and resonance of the rotor system, a sensitivity study of the frequency reliability of the system is conducted. The technique developed utilizes random perturbation technology, reliability theory, and sensitivity technology. The reliability mode and the failure probability of the rotor systems are defined. The second-order joint failure probability is obtained using numerical integration methods. The variation regularities of the reliability are obtained and the influences of random parameters on the reliability of the rotor system are studied. The method presented provides a theoretical basis for the frequency reliability sensitivity design of the rotor system. A numerical example is analyzed to show the effectiveness of the proposed method.