Satellites formation design in unperturbed eccentric reference orbit was presented. Relative motion problem was discussed in RAC coordinate system. The relationship of orbital element differences and deputy satellite coordinates in RAC was established using the sensitivity matrix in RAC

and arithmetic of formation design in eccentric orbit was also deduced. Using the arithmetic

chief-deputy same trace formation flying orbit was designed. Simulation shows that the position error is measured by millimeter

and velocity error is measured by millimeter/second. The precision of the arithmetic can satisfy the need of formation flying mission.