The invention relates to the technical field of rail vehicles, and particularly to a sandbox anti-falling seat vibration impact testing device of Multiple Units and a method thereof. The sandbox anti-falling seat vibration impact testing device comprises two first supporting units and one second supporting unit. Each first supporting unit comprises a first transverse supporting beam for supporting a sandbox. Furthermore the connecting part between the first transverse supporting beam and the sandbox is provided with a height-adjustable adjusting gasket. The second supporting unit is provided with a frame mounting beam, a sandbox mounting beam for mounting the sandbox, and an anti-falling seat mounting frame which is connected with the frame mounting beam and is used for placing an anti-falling seat. The anti-falling seat mounting frame is arranged below the sandbox mounting beam. The sandbox anti-falling seat vibration impact testing device has advantages of simple structure, high convenience in mounting, and flexible adjustment for distance between the sandbox and the combining force of the anti-falling seat, quick and efficient clamping positioning in vibration impact testing of the sandbox anti-falling seat, high reliability in testing controlling, and high accuracy of testing data.