Abstract: In order to evaluate the effect of BeiDou satellite system(BDS) D2 navigation message to signal in space (SIS) integrity, the BeiDou D2 navigation message was researched in the structure and the content. At first,Through the analysis of basic navigation information, the message and time used in the process for determining satellite position and user position were given. Simultaneously, the user ranging error which influenced by satellite ephemeris and clock was illustrated, the ionosphere and tropospheric error correction model were introduced either. Then, through the analysis of enhanced service information, the calculation method of integrity information (RURA, UDRE) and grid ionospheric delay were discussed. Finally, the calculation method of protection level (PL) for user positioning error that use integrity information and user local error was given.

Key words: BeiDou, Navigation message, Integrity, Protection level