In order to improve the automation level and the efficiency of transmission tests,a transmission test rig is designed based on the electric power close-loop technology.SIEMENS S7-400 PLC plays the role of main controller in the measurement and control system,and is connected with 6RA70 DC motor driver,human machine interface developed by WinCC configure software by Profibus field bus.PLC controls the motor according to the relationship between set value and reference value,in this way,torque and speed can be loaded smoothly and adjusted continually to emulate the operation condition of the transmission.Accuracy of the data acquisition is improved by incorporated the zero compensation and Kalman filter.Test results indicated that the control system has the property of high accuracy,easy-operating,stablity and reliability.