Due to the spectrum congestion of current navigation signals in L band, C band has been taken into consideration as a candidate frequency band for Global Navigation Satellite System (GNSS). However, the compatibility between navigation signals in C band and the existing signals in adjacent frequency bands must be carefully analyzed before any new band for satellite navigation is put into use. The radio astronomy (RA) band and microwave landing system (MLS) band are adjacent to C band, in order to evaluate the compatibility and interference between these signals, interference analysis between the C band which would be used for satellite navigation service and RA/MLS are proposed. The compatibility assessment rule by comparing the maximum of the power flux density (PFD) of the navigation signals in C band with the PFD threshold of RA and MLS is utilized. Simulation results show that this new type of signal modulation named as MSKBCS2 is more suitable considering the interference out of band of C band to RA/MLS. In addition, the restriction of the leak out of C band from the RA is more stringent. Consequently the navigation service in C band is more compatible with MLS compared with RA.