A robotic external fixation system for the surgery of bone deformity correction was developed to simulate the execution process of fractured femur by the adjustment of the joints of the fixation system. An inverse kinematics analysis algorithm was developed to calculate the necessary rotations and translations at each joint of the robotic system. The computer graphic model was developed for validation of the analysis result and visualization of the surgical process. For given rotational and angular deformity case, the surgical execution process using the robotic system was well matched with the pre-operative planning. The final residual rotational deformities were within 1.0-1.6 degrees after surgical correction process. The presented robotic system with computer-aided planning can be useful for knowledge-based fracture treatment and bone deformity correction under external fixation