Abstract: It is known that the Unscented Kalman filter (UKF) is applied in X-ray pulsar navigation because of the high nonlinearity of its state equation and measurement equation. In order to improve the computational efficiency of standard UKF, the method to get sample points in UKF is modified in this paper. As a result, the state update could be done by integration needed only one time. Moreover, the equivalency of standard UKF and modified UKF is proved in the work. The simulation results demonstrate that the computational efficiency of modified UKF could be 5 times higher than that of standard UKF with the same condition of computation precision:the position determination precision is about 70 meters and the velocity determination precision is about 0.005 meters per second.