Abstarct: Today, legged-robots are the subject of interest by researchers. Due to their basic design, legged-robots, avoid obstacles on floors, and therefore provide more useful service for human being. Bipeds are one of the legged-robots and the most important problem of them is to find a stable trajectory for their movement. In many studies, bipeds are analyzed as a planer robot and in there, toe rotation is not considered. In this thesis with a view to approach to human legged movement, the biped is considered with active toe rotation and as a 3D model. A common criteria used in stability analysis of bipedal robots, is the Zero Moment Point criteria which is also used in this thesis. In this thesis, first the two-legged robots, history, features, principles and common phrases associated with them are discussed. Also there’s a glimpse to the Curves of the human motion in order to better understanding the walking method. Then with use of the Zero Moment Point constrain, the stable trajectory of gaits for a 9 lixnk robot is designed. To create longer strides, humans use a phase in which the foot is rotated about its toe. So in this thesis a gait type is used which the entire sole of the support foot, first touches the ground but then it rotates about its mextatarsal axis as an active joint. For solving of the equations of motion of the Robot, is used a fiction Zero Moment Point as a virtual constrain. With this method, the basic acceptable equation is obtained for robot movements and by using an algorithm, trajectory for joints is calculated. Then with examination of Zero Moment Point and by using another algorithm, the desired trajectory of the biped is obtained. Finally, by using the computed torque control method, the trajectory of the robot joints in order to have stable gait are tracked. The coefficient of proportional and derivational of this controller is calculated with help of particle swarm optimization algorithm which is spired from animal society's life.