Abstract: Accordingtothedefinitionofsignalinspaceuserrangeerror(URE)andtherootmeansquareURE(rmsURE)calculationmethodgivenintheGlobalPositioningSystemStandardPositioningServicePerformanceStandard(GPS-SPS-PS),theBeiDouNavigationSatelliteSystem(BDS)instantaneousURE(IURE)andrmsUREformulaswerededucedconsideringtheelevationconstrains.Inaddition,BDSUREwascalculatedbytheephemerisdata,andtheBDSreceiverrawobservations.Theresultsshowthatthetwomethodsmatchwell,andbotharelessthan2.5metersinthecaseof95%confidencewhichmeetsthebasicrequirementsofthesignalinspaceUREgivenintheBDSopenserviceperformancestandard(BDS-OS-PS).

Key words: BeiDouNavigationSatelliteSystem, signalinspace, instantaneoususerrangeerror, rootmeansquareuserrangeerror, pseudo-rangeobservationequation