Abstract: An introduction on broadcast ephemeris parameters fitting for GEO satellites based on coordinate transformation is presented. The formulas of the relationship between the new instantaneous orbital elements as well as their perturbation and that before coordinate transformation are derived, and influence of difference inertial coordinate (different X-Axes orientation or different rotation angle) is analyzed. Experiments for broadcast ephemeris parameters fitting from simulated GEO orbit data are conducted to analyze the impact of different rotation angular adopted on the fitted ephemeris parameters. Our analysis and experiments show that: first, the inclination angle of the orbit obtained by simplified coordinate transformation is not constant but subject to periodic variation. Second, the perturbation of inclination angle in original frame may be magnified and then absorbed by the perturbation of inclination angle and perigee in the new coordinate system, while the magnification varies from tens to thousands and sometime singularity happens. Third, the range of some fitted GEO broadcast ephemeris parameters such as “Mean Motion Difference From Computed Value” and “Rate of Right Ascension” gradually decrease as the rotation angle increases