Due　to　the　high　viscosity　and　poor　mobility,　it＇s　difficult　to　measure　the　viscous　oil　well　accurately　with　traditional　test　separator.　Besides,　viscous　oil　wells　have　a　wide　range　of　flow　rates,　often　from　several　to　thousand　barrels　per　day,　while　the　GVF　varies　from　0　to　80%.　So　few　measuring　devices　are　able　to　test　viscous　wells.　To　address　this　issue,　this　paper　proposes　a　method　for　oil-water-gas　measurements　in　heavy　oil　applications,　which　covers　a　wide　flow　range.　It　includes　a　Venturi　meter,　a　dual　gamma　sensor　and　a　mini　separator　equipped　with　a　differential　pressure　transmitter　(DPT).　When　the　viscous　oil　flow　rates　are　in　the　measuring　range　of　Venturi,　a　proper-sized　Venturi　and　a　dual　gamma　sensor　are　used　to　measure　the　flow　rates　of　oil,　water　and　gas,　respectively.　Since　the　viscous　oil　is　flowing　with　low　Reynolds　number,　a　suitable　model　was　established　to　calculate　the　discharge　coefficient　of　the　Venturi.　When　the　multiphase　flow　rate　falls　outside　the　low　limit　of　the　Venturi　meter　or　it　is　an　intermittent　flow,　the　liquid　mass　flow　rate　can　be　obtained　through　a　mini　separator,　where　the　liquid　accumulates　and　generates　differential　pressure　across　the　separator.　Combing　with　gamma　sensor,　we　can　get　the　flow　rates　of　oil,　water　and　gas　respectively.　In　this　method,　gamma　rays　technology　is　used　to　conduct　the　phase　fraction　measurement　more　accurately.　This　technology　is　independent　of　viscous　oil　flow　patterns　such　as　emulsion.　Coupling　with　the　weighing　method　through　the　mini　separator,　a　full　range　on-line　measurement　of　oil,　water　and　gas　in　viscous　oil　can　be　realized.　The　experiments　on　a　prototype　meter　(2　inch　Venturi　and　DN50　piping)　made　by　this　method　were　carried　out　in　a　multiphase　test　loop.　The　test　results　indicate　that　the　measurement　standard　deviations　of　liquid　flow　rate,　WLR　(water　to　liquid　ratio)　and　gas　flow　rate　are　4.2%,　1.5%　and　6.3%,　respectively.　©　2016,　Editorial　Office　of　Journal　of　Xi＇an　Jiaotong　University.　All　right　reserved.