Abstract: To eliminate significant vibration of motors in oil pumps, portable vibration analyzer is used to acquire operation parameters of motors and then working conditions of such motors are graded. Results of assessment on vibration intensities show that vibrations of motors are classified as Grade C in accordance with relevant national standards. Consequently, such motors should not operate in a prolonged continuous manner. Results of frequency-spectrum and velocity reduction analyses show that such motors are highly vulnerable to electric failures. Specific inspections are conducted for seating and anchor bolts of such motors, the revealing causes for failures show that, there are weak support at No.6 point and slight deformation on external shell of the motor, which led to eccentricity of the stator and subsequently severe vibration. Actual inspection results have verified the above diagnosis results.