Abstract:  This article is to study the relative positioning accuracy of Bll/B2a of BeiDou-3 NavigationSatellite System (BDS-3 ). The data of 10 Multi-GNSS Experience (MGEX) tracking stations in Austral.ia were processed by GAMI'T software. The experimental results showed that the maximum standard devia-tion (STD) of Global Navigation Satellite System(GLONASS)G1/G2 north(N), east (E), length(L) baseline vectors reached 8.00 mm, 12. 10 mm and 10. 60 mm , respectively; the maximum standard eviation of up ( U) baseline vector of BeiDou-2 Navigation Satellite System ( BDS-2) B1l/B2I is 28. 70mm. The baseline length was positively correlated with the standard deviation ( STD) of baseline length.The mean square error and weighted root mean square (WRMS) of BDS-3 B1l/B2a, Galileo satellitenavigation system ( Galileo) E1/ESa and Global Positioning System ( GPS) L1/2 are generally small.with high accuracy ; BDS-2 Bll/B2l and GLONASS Gl/G2 are relatively large and low in accuracy. Theexperimental results further show that the positioning precision of BDS-3 Bll/B2a has been greatly im-proved compared with that of BDS-2 B1/B2I.

Key words: BeiDou-3 navigation satellite system, standard deviation of baseline vector, standard devia-tion of baseline length, mean square error of point position, weighted root mean square