Abstract: Based on an introduction to the mechanical structure and operating principle of the load simulator drived by the direct current torque motor, a mathematical model of the actuating mechanism of the electrical loading system was founded and was expressed by means of block diagram. The mechanical characteristic of the direct current torque motor and the operating range were studied. The production mechanism of the extraneous torque during the start-up, operating mode and reversing of the motor-drive load simulator was analyzed. A method of feedforward compensating the extraneous torque based on the principle of structure invariance was promoted. The result of the simulation shows theoretically that the feedforward compensating can reduce the interference caused by the extraneous torque effectively. The feasibility and effectivity of the method are also proved by experiments.