Abstract: Recently the research of Satellite Formation Flying (SFF) has increased significantly. The characteristic and potential advantage of SFF is that several following-satellites along with the leader-satellite in close vicinity make up a special formation to accomplish certain mission. The Relative Trajectory (RT) is defined as the geometric pattern consisting of the centroid of each satellite, and the RT design is to find out those orbit elements of each satellite according to the geometric pattern of the RT (the orbit elements of leader-satellite can be determined by performing mission first). A concept of natural formation and a general RT design method are proposed based on the Relative Orbital Element Method and the relative motion equation in this paper. An example is given.