A new method called Unscented Kalman Filter (UKF) is used for tracking targets. It doesn't make errors from simplifying complex models like other methods. The UKF improves accuracy and is easy to use. The UKF based on square root decomposition (SRD-UKF) is introduced in this paper. It is more stable and ensures better estimates than other methods like UKF and PF, as shown in a simulation experiment.