The anti-gravity gait training system is a rehabilitation training device for patients with neurological impairments and elderly people having problems with walking. We are developing a unloading body weight device for the gait training system. Unloading device is a necessary part because the user of this system have a muscular skeletal weaknesses. We want to control the unloading forces to be steady because the physiological gait pattern can be obtained in this condition only. We have developed the simulation model of gait training system, a human dummy models, various traditional unloading devices and the controlled unloading device. Simulation model will be used for designing a novel controller and mechanism of unloading system.