Abstract: The safety of close formation flying satellites was investigated. Aiming at the near round reference orbit satellites,the formation configuration was described based on the relative orbit elements,formulas of the minimize distance of formation flying satellites in the cross-track direction were proposed,and the influence of J2 perturbation to the safety of satellites formation was analyzed. The simulation results demonstrate that the phase difference in the orbital plane and the plane perpendicular to the orbital plane has great impact on the safety of the close formation flying satellites. The measures which can make the formation satellites safer have practical value for enabling the satellites formation.