With the rapid growth of the technologies of vehicles and tracking， this paper proposes an approach of optical satellites tracking an extraatmospheric vehicle based on unscented Kalman filter （UKF） under the background of satellite constellation tracking vehicles. It solves the problem of optical satellites tracking an extraatmospheric vehicle accurately and velocity estimation error converging rapidly within 30 s in the case of reasonable observation distance. The validity of this algorithm and relative superiority to EKF are verified by simulation.