The invention discloses a transmission system gearbox reliability test bed of a high-speed multiple unit. The transmission system gearbox reliability test bed of the high-speed multiple unit comprises an L-shaped bearer platform power flexible driving torque tester, a rectangular bearer platform power flexible driving torque detection tester, a trial gearbox assembly tester and a three-DOF (degree of freedom) vibration simulation test device, wherein the trial gearbox assembly tester and the three-DOF (degree of freedom) vibration simulation test device are mounted in parallel on the foundation, and a trial gearbox in the trial gearbox assembly tester is connected with a tested gearbox in the three-DOF (degree of freedom)vibration simulation test device through a synchronous universal joint coupling of a ball cage type. The L-shaped bearer platform power flexible driving torque tester is connected with the trial gearbox assembly tester trough a cross axial universal coupling, and the rectangular bearer platform power flexible driving torque detection tester is connected with the three-DOF (degree of freedom) vibration simulation test device through the cross axial universal coupling.