Abstract: In view of the service performance evaluation of BDS constellations in the peripheral sea areas of our country at the present stage， the constellation usability and constellation coverage assessment index and calculation formula are given， and a systematic test and analysis of the Pacific Ocean and Indian Ocean assessment sea areas based on grid partition is made. The assessment data shows that the BDS constellation has been qualified above 60°S~60°N， 150°～180°E and 60°S ～30°N， 40°～70°E sea areas. The assessed sea areas have a longitude from 150°E to the east and 70°E to the west. At low latitudes， the performance of BDS constellations gradually deteriorates. The performance of BDS services in some sea areas and some epochs can reach excellent and good levels. The result of the assessment confirms that the BDS constellation achieves sea level performance at all levels of sea service which can be taken as reference for the expansion of BDS applications at sea．