Abstract: In order to meet the test requirements of main reducer of helicopter transmission system with single engine and double engine input,improve the utilization,versatility,convenience of equipment,and reduce the energy consumption of the system,the electric power closed structure should be adapted to design the main reducer tester. Taking the double engine input configuration as an example,the structure of the system is analyzed,the control technology and mode are introduced,and the speed loop saturation and torque limiting control technology are introduced to meet the technical requirements of the tester.