In order to accurately calculate the deflection of permanent magnet synchronous motor (PMSM) rotor and reduce the production cost of motor, the eccentric electromagnetic force and deflection of the rotor are analyzed and calculated based on theoretical analysis and finite element method. The analytical expression of unbalanced magnetic pull of PMSM is derived, and the finite element calculation methods of unbalanced magnetic pull and rotor deflection are introduced in detail. Taking a 355 kW 1 500 r/min PMSM as an example, the calculation results of finite element method and analytical method of unbalanced magnetic pull and rotor deflection are compared, which verifies the reliability of finite element method and has certain reference significance for the accurate calculation of rotor machinery and the study of vibration and noise of PMSM.