The invention discloses a gear shifting-down impact testing method of a torque backlash type gearshift mechanism. The method comprises the following steps of S1, adjusting a pretightening force of each elastic component to zero, or detaching all elastic components; S2, connecting an input shaft with a driving motor, and connecting an output shaft with a dynamometer; S3, setting a torque loading parameter and a highest cyclic loading number-of-times Nmax of the dynamometer; S4, setting experiment ending conditions of a, faults of abnormal sound, abnormal vibration or power transmission failureof the torque backlash type gearshift mechanism, and b, the cyclic loading number-of-times Nx of the dynamometer satisfies a condition Nx=Nmax; and S5, starting the driving motor and the dynamometer,and ending the experiment when a random condition in the step S4 is satisfied. The gear shifting-down impact testing method has advantages of great testing device simplification, low cost, accurate and reliable testing result, and high testing efficiency.