Abstract: In practical applications,some measurement equipment(such as laser) of satellite formation flying can not be used for mission requirements,which led to the decline in observability.The condition number was used in quantitative calculation of the observability in satellite formation flying system.For satellite formation flying orbit adjustment situation,which only used radio measurement,a strong tracking unscented Kalman filter(UKF) algorithm was introduced to the simulation.The results show that the method has strong tracking capability,robustness and stability.Moreover,a strong tracking UKF algorithm has similar accuracy with that of the normal UKF algorithm.