Abstract: The mean orbit elements play an important role in sate ll ite orbit design and constellation simulation On the basis of the domestic and overseas research results,a simplified but practical mutual transform between os culating orbit elements and mean orbit elements is given,which has no singularit y The practice in the constellation design and simulation demonstrates that this method is well and truly useful By taking advantage of the mean orbit elements,an interesting result is also given about the circular orbits in the equator plane