Abstract: Radio occultation can provide the ionospheric electron density profile from the ground to the height of LEO orbit, which play an important role in the research of topside ionosphere. In this paper, COSMIC (Constellation Observing System for Meteorology Ionosphere and Climate) radio occultation data are used to obtain the electron density profile, and the ionospheric parameters, such as hmF2 (peak height of F₂ layer), NmF2 (peak electron density of F₂ layer), VSH (vertical scale height), are extracted. The changes of F2 layer in Antarctica are studied in the solar activity cycle, annual cycle and diurnal cycle, respectively. The vertical structure characteristics of top ionosphere in Antarctica, especially for Weddell Sea anomaly, are studied in detail. The results show that the daily averages of the whole Antarctic hmF2, NmF2 and VSH are 250 km, (1-4)× 10¹¹el/m³, 100~200 km, respectively, during low solar activity, and up to 250-300 km, (1-8)× 10¹¹el/m³, 150-250 km, respectively, during high solar activity. Weddell Sea Anomaly is mainly characterized by the electron density enhancement at the top and the electron density reduction at the bottom, which lasts four months, from late spring to early autumn.