In the background of "strong direct and weak AC" power grid, the condenser with dynamic reactive power support capability is becoming more and more important, and its operation safety and stability will become the focus of future research. Due to manufacturing, installation, operation and other reasons, the air gap eccentricity fault of the condenser rotor occurs frequently, causing serious harm. Taking the air gap eccentricity fault of the condenser rotor as the research object, this paper deduces the variation rules of the air gap flux density before and after the eccentricity, the unbalanced magnetic pull force of the rotor and the circulating current of the stator. It is found that the air gap magnetic density produces even harmonics after the eccentricity, which causes the rotor vibration, and the stator parallel branches generate circulating current. The static eccentricity and dynamic eccentricity have difference in the rotor vibration frequency and branch circulating current At the same time, based on the structural parameters of a 300 Mvar large-scale condenser, the finite element model is established by using Ansoft software, and the correctness of the fault compound feature analysis is verified by simulation, which provides reference and guidance for the fault diagnosis and safe and stable operation of the condenser.