The objective of this study was to propose the walking in water for ACL injury rehabilitation program by simulation. For this objective, the simulator which can compute the body load considering the fluid force and force acting on the ACL was utilized. The optimal walking forms for three rehabilitation phases were then computed by the simulation. From the simulation analysis, the form for the first phase of rehabilitation was obtained as “bend the knee all through the swing phase”. This form can prevent the ACL from loading the force. The form for the second phase was obtained as “bend the knee greatly and stretch the ankle first, then bend the hip keeping the knee bent and the foot stretched in the swing phase”. By this form, the muscles around the knee joint can be trained without loading force on the ACL. The form for the last phase was obtained as “keep the thigh backward and the ankle stretched first, then bend the hip joint quickly and greatly in the swing phase”. By this form, the muscles around the knee joint can be trained to the utmost.