The paper firstly introduced the composing and the theory of the vehicle transmission loading test stand based on secondary regulation technology. The test stand includes speed control system and torque control system. Then the theory of these two control systems is illuminated and theirs mathematic models is established in the paper. When there are multi subsystems in the whole system, it would be some coupling among the subsystem. The paper analyzed the influence that the torque control system acts on the speed control system. When the external interference torque is constant, it makes little influence on the other control system. But when it is variational, it has big influence on the speed system. The traditional close loop control has little performance on the coupling between the two systems. Then the feed-forward compensation control is put forward to eliminate or reduce the coupling. The simulation result proved that the feed-forward compensation control is a good way to solve the coupling between speed control system and torque control system.