The invention discloses a power closed testbed for the running characteristic of an overloading coupler. The power closed testbed comprises a left gearbox, a right gearbox, a testing piece and an accompany test piece. A closed transmission system is formed between the left gearbox and the right gearbox through the testing piece and the accompany test piece and is provided with a motor used for providing power and power compensation, rotating speed and rotating torque sensors are arranged at the two ends of the testing piece, and a hydraulic loader used for providing loads is arranged on the closed transmission system. Through the reasonable design, the testing requirement for the overloading coupler under the condition of the large inclination angle and the low-speed overloading or high-speed underloading work condition can be met at the same time, the cost is lower than that of the running characteristic testing experiment of a coupler of the same specification, meanwhile, testing efficiency is improved, and the testbed has the advantages of being simple in structure, convenient to operate and wide in application range.