Determined to become a new member of the well-established GNSS family,COMPASS(or BeiDou-2) is developing its capabilities to provide high accuracy positioning services.Two positioning modes are investigated in this study to assess the positioning accuracy of COMPASS’ 4GEO/5IGSO/2MEO constellation.Precise Point Positioning(PPP) for geodetic users and real-time positioning for common navigation users are utilized.To evaluate PPP accuracy,coordinate time series repeatability and discrepancies with GPS’ precise positioning are computed.Experiments show that COMPASS PPP repeatability for the east,north and up components of a receiver within mainland China is better than 2 cm,2 cm and 5 cm,respectively.Apparent systematic offsets of several centimeters exist between COMPASS precise positioning and GPS precise positioning,indicating errors remaining in the treatments of COMPASS measurement and dynamic models and reference frame differences existing between two systems.For common positioning users,COMPASS provides both open and authorized services with rapid differential corrections and integrity information available to authorized users.Our assessment shows that in open service positioning accuracy of dual-frequency and single-frequency users is about 5 m and 6 m(RMS),respectively,which may be improved to about 3 m and 4 m(RMS) with the addition of differential corrections.Less accurate Signal In Space User Ranging Error(SIS URE) and Geometric Dilution of Precision(GDOP) contribute to the relatively inferior accuracy of COMPASS as compared to GPS.Since the deployment of the remaining 1 GEO and 2 MEO is not able to significantly improve GDOP,the performance gap could only be overcome either by the use of differential corrections or improvement of the SIS URE,or both. COMPLETED (or BeiDou-2) is developing its capabilities to provide high accuracy positioning services. Two positioning modes are investigated in this study to assess the positioning accuracy of COMPASS ’4 GEO / 5IGSO / 2MEO constellation. Precise Point Positioning (PPP) for geodetic users and real-time positioning for common navigation users are utilized. To evaluate PPP accuracy, coordinate time series repeatability and discrepancies with GPS ’precise positioning are computed. Experiments show that COMPASS PPP repeatability for the east, north and up components of a receiver within mainland China is better than 2 cm, 2 cm and 5 cm, respectively. Apparent systematic offsets of several centimeters exist between COMPASS precise positioning and GPS precise positioning, indicating errors remaining in the treatments of COMPASS measurement and dynamic models and reference frame differences existing between two systems. For common positioning u sers, COMPASS provides both open and authorized services with rapid differential corrections and integrity information available to authorized users. Our assessment shows that in open service positioning accuracy of dual-frequency and single-frequency users is about 5 m and 6 m (RMS), respectively, which may be improved to about 3 m and 4 m (RMS) with the addition of differential corrections. Let accurate Signal In Space User Ranging Error (SIS URE) and Geometric Dilution of Precision (GDOP) contribute to the relatively inferior accuracy of COMPASS as compared to GPS .ince the deployment of the remaining 1 GEO and 2 MEO is not able to significantly improved GDOP, the performance gap could only be overcome either by the use of differential corrections or improvement of the SIS URE, or both.