Abstract: Radio Occultation (RO) technique has become a powerful method to remote sense the Earth's atmosphere and ionosphere since GPS/MET program. The ionospheric electron density profile (EDP) can be retrieved by the Abel inversion from the RO measurements. The Abel inversion has degraded performance in the area with large horizontal gradients because of spherical symmetry assumption. With the increased number of RO satellites in the future (e.g., possible 12 satellites in COSMIC 2), it is possible to retrieve the EDP by assimilating both the dense ground and LEO based GNSS observations simultaneously. In this study, we will test: (1) retrieve RO aided by the global ionospheric map (GIM) products provided by the IGS and (2) assimilative retrieve RO by incorporating ground based GNSS slant TEC data. Both the simulation and real data retrieval will be done to evaluate improvement performance in comparison with Abel method. The data process (ground GNSS, LEO RO), error analysis, and assimilation method will be described.