The invention discloses a test bench for the reliability of a U-shaped desk-type transmission system of a gear box of a motor train unit, and aims at solving a problem that a reliability test of a bearing of an axle box of a transmission system of the motor train unit cannot be carried out. The test bench comprises a gear box test vibration shaft assembly, a narrow U-shaped platform assembly, an arc-shaped seat assembly, a front cross-shaped guide rail supporting seat, and a rear cross-shaped guide rail supporting seat. The narrow U-shaped platform assembly is disposed on a foundation. A left arc-shaped seat assembly and a right arc-shaped seat assembly of the arc-shaped seat assembly are disposed on the foundation at two sides of the narrow U-shaped platform assembly. A U-shaped upper angle platform of the gear box test vibration shaft assembly is disposed on a narrow U-shaped platform of the narrow U-shaped platform assembly and locked. A left motor assembly and a right motor assembly of the gear box test vibration shaft assembly are sequentially connected with an inner side of the arc-shaped seat assembly. One end of the front cross-shaped guide rail supporting seat and one end of the rear cross-shaped guide rail supporting seat are disposed at the front and rear ends of a right platform. The other end of the front cross-shaped guide rail supporting seat and the other end of the rear cross-shaped guide rail supporting seat are disposed at the front and rear ends of the narrow U-shaped platform.