Abstract: Focusing on the needs of harmonic reducer bearing life test, a harmonic reducer bearing test device was built, combined with the harmonic reducer bearing test principle, the harmonic reducer bearing test conditions were determined by calculating the average input speed and average load torque, and the load torque control method was established based on the expansion state observer and nonlinear PID. According to the experimental results, it is concluded that the root mean square error of load torque tracking is 0.375, which has good control accuracy, and the testing machine realizes high-precision control of speed and load torque, realizes temperature rise, vibration, noise and other index tests, and meets the test requirements of harmonic reducer bearings.