Abstract: To study the motion of formation flying satellite in one orbital period,the J2 instant perturbation model was derived based on the perturbation acceleration theory.To explore the effect of J2 instant perturbation,a SSO Satellite and a two-satellite formation were taken as examples.Compared with the J2 average perturbation model,for the satellite in one orbital period,the semi major axis had an error of 18km,the eccentricity had an error of 10-3,and the orbit inclination angle had an error of 10-2 degree.And for the formation in one orbital period,the relative radial position offset was 5km,the relative ink-track position offset was 19km,the relative normal offset was 10-2,and the relative distance offset was 19km,and they grew with time went on.