Abstract: For large induction motor, eccentricity problem is one of classical faults. At the same time, eccentricity leads to the degradation of motor’s performance. It’s meaningful to study eccentricity problem of large motor. Curved eccentricity is mostly appeared due to elasticity modulus of the material. However, there are sorts of factors causing curved eccentricity, mainly including gravity of rotor part, centrifugal force and the unbalanced magnetic pull(UMP). The calculation of deflection is based on approximately differential equation of the deflection curve in mechanics of materials. In addition, dynamic UMP calculation is established and UMP will be of no big deal to eccentricity deflection in induction motor according to the calculation below. The formation of curved eccentricity is explained and three kinds of forces carried on rotor quantitatively are compared. Furthermore, the final curve equation is figured out. Among the calculation, finite element analysis is used to calculate UMP force accurately.