The invention discloses a device and a method for detecting a speed changer. The device comprises a central processing unit, a display screen, a key group, a driving motor, a speed reducer, a torque sensor, an inertia disc, a load motor, a first rotating speed sensor arranged on the driving motor and a second rotating speed sensor arranged on the load motor, and is characterized in that the driving motor is connected with the input end of the speed reducer, the output end of the speed reducer is connected with an input shaft of the speed changer through a coupling, an output shaft of the speed changer is connected with the input end of the inertia disc through a half shaft, the output end of the inertia disc is connected with the load motor, the torque sensor is arranged on the half shaft, and the central processing unit is electrically connected with the display screen, the key group, the driving motor, the speed changer, the torque sensor, the load motor, the first rotating speed sensor and the second rotating speed sensor respectively. According to the invention, which range the rotating speed difference of a synchronizer is required to be when a double-clutch speed changer applied to a hybrid power automobile can shift normally can be detected.