The utility model discloses a reliable test bench for a high-speed motor train unit transmission system assembly, which comprises a power transmission flexible test device, a three-degree of freedom vibration simulation test device and a reliable test device for the high-speed motor train unit transmission system assembly, wherein the three-degree of freedom vibration simulation test device and the reliable test device for the high-speed motor train unit transmission system assembly are arranged on a foundation side by side; the parallel distance between a beam in the three-degree of freedom vibration simulation test device and a bearing platform of the high-speed motor train unit transmission system assembly in the reliable test device for the high-speed motor train unit transmission system assembly is between 20 and 40 millimeters, and a work surface of the beam and a work surface of the bearing platform of the high-speed motor train unit transmission system assembly are on the same horizontal plane; and the three-degree of freedom vibration simulation test device is connected with the power transmission flexible test device arranged on the foundation by a transverse actuator, and the power transmission flexible test device is connected with the reliable test device for the high-speed motor train unit transmission system assembly by a cross axle universal coupler.