The utility model provides a testing machine for fault diagnosis of a hydraulic system and relates to the testing machine. In the prior art, the fault diagnosis of the hydraulic system is manually troubleshot, the efficiency is low, and the risk is high. The testing machine is characterized by comprising a machine case and a hydraulic system, wherein the hydraulic system comprises an electric motor, a hydraulic pump, a one-way valve, a pressure regulating valve, a pressure meter, a reversing valve, a filter, a first joint, a second joint and a third joint, the hydraulic pump is connected with the electric motor, an oil outlet of the hydraulic pump is connected with an oil inlet of the one-way valve through an oil pipe, an oil outlet of the one-way valve is respectively connected with an oil inlet of the pressure regulating valve, the pressure meter, an oil inlet of the reversing valve and the third joint through oil pipes, an oil outlet of the pressure regulating valve is connected with an oil inlet of the filter, a work oil opening of the reversing valve is respectively connected with the first joint and the second joint, and an oil outlet of the reversing valve is connected with the oil inlet of the filter through an oil pipe. The testing machine adopting the technical scheme has the advantages that the structure is simple, a hydraulic oil cylinder and a hydraulic motor can be tested under an off-line state, and the work is flexible, convenient, safe and reliable.