In recent years several studies have been done in order to improve standing power and gait performance in Spinal Cord Injury (SCI) patients.SCI patients can regain their standing power and gait ability with orthopedics tools that called Orthosis, these tools are divided into two groups: passive and active orthosis. These tools can provide necessary support for these patients which depend on the level of spinal damage. in this thesis first, a passive Hip-Knee-Ankle-Foot Orthosis (HKAFO) has been studied then the improvement of standing performance in hands-free mode (without using Canes and crutches) is discussed. To achieve stability in a hands-free stand mode, patients can lean to upper section of orthosis (TLSO) and restore its own stability. In this standing posture, patients are inclined to TLSO that called C posture. Comparing the way of standing in SCI patient with healthy person and the limitations of SCI patients to use its own hands, it can be inferred that this way of standing is not proper. To maintain the correct position standing it is necessary to upper body alignment in a similar manner of healthy person. In order to achieve this goal, installation of the actuator on the Orthosis hip was evaluated to help the patient stand in the correct mode and by the usage of upper body movement patient can restore the stability mode. For the installation of actuator, the person with Orthosis is modeled in four-linked (three-link lower limb and a single link upper body with hands) serial system. With the kinematic constraint considered for the feet, standing sustainability and stability torque limitations applied to the upper body in order to obtain the stability and suitability was calculated. For optimization operation of actuator, the appropriate location of hip was calculated and according to the result, the fixed angle of lower limbs Orthosis and the equilibrium point center of upper body has been resulted. In order to achieve sustainability and stability of upper body, two controllers had been designed and by using simulation analysis, their performance was studied. At the end the five-link Orthosis and the SCI patient which the lower limbs was fixed with Orthosis and reduced to two degree freedom model. Otherwise with the simulation model operative of controllers and actuators for stability establishment in known movements of hand had been studied. Keywords: Spinal cord injury, orthosis, quiet standing, dynamic standing, stability