An approximate kinetic equation describing an object following a near-circular ellipse trajectory is given in Lhis paper. Based on the orbit parameter of the GRACE satellites and under the condition that no consideration was given to the disturbance acting on the satellites, the authors calculated the distance, the relative velocity, and the inclination of the twin satellites, and analyzed their influence on the K-band ranging system. Theoretical analysis shows that the double frequency effect of the ellipse orbit could help to test the distance and velocity measurement of the K-band ranging system in orbit, which is of significance in the research and development of the K-band ranging system.