In recent years, Treadmill Body Weight Support System has been developed and proved the improvement for patients who recover from Spinal Cord Injury. Passive and dynamic systems were shown their capacities to maintain unloading force in the vertical direction, however, there are no system considered that track the moving of the Center of Pressure trajectory during gait training. Our hypothesis is that tracking Center of Pressure trajectory, during gait training, could be more effective than the common system. This paper proposed a new active Body Weight Support system using Pneumatic Artificial Muscle actuators. An active model of new Body Weight Support system with the tracking model of the human center of pressure was developed. The validation tests experiments were implemented with three levels of unloading force 30%, 50% and 70% using new Body Weight Support system and counter weight system for comparison. The speed of the treadmill is set, for all the experiments at 2 km/h. Center of pressure trajectories are recorded for a normal random walk, for the counter weight system and for the Body Weight Support systems. The results showed that the center of pressure trajectory using active system was much fitter with center of pressure pattern of normal gait than counter weight system.