The invention relates to a testing device and testing method of a steering gear. The testing device comprises a computer, a manipulator that is held at a motor and is used for moving the motor, a probe that is used for striking a synchronous belt to excite the synchronous belt to make vibration and sounds, a belt tension tester for detecting the acoustic frequency of the synchronous belt, a centerconnected to an output shaft of the motor, a displacement sensor that is arranged on the center and is capable of detecting the displacement of the output shaft of the motor, and a positioning clampfor keeping a housing of a steering gear to be fixed. The manipulator, the belt tension tester, and the displacement sensor are respectively connected with the computer; and the computer is able to calculate the tension force corresponding to the synchronous belt according to the acoustic frequency, detected by the belt tension tester, of the synchronous belt. According to the testing device, whenthe motor and the housing of the steering gear are assembled, the tension of the synchronous belt is ensured; and the distance between the center axis of the motor and the center axis of a lead screwis measured precisely.