A　high-precision　testing　bench　is　required　for　accurately　assessing　the　dynamic　Transmission　error　(TE)　of　precision　reducers.　However,　the　relationship　between　the　testing　bench＇s　accuracy　and　deviations　in　testing　conditions　has　not　been　determined,　leading　to　an　inaccurate　evaluation　of　its　metrological　performance.　In　this　study,　we　examined　the　accuracy　characteristics　of　the　testing　bench.　We　analyzed　the　structure　of　the　bench　and　identified　the　main　error　sources　that　affect　its　accuracy,　including　mechanical　system　deviation,　sensor　measurement　deviation,　and　testing　condition　deviation.　In　addition,　we　studied　the　mechanism　of　these　error　sources　and　proposed　a　method　to　convert　drive　speed　deviation　and　load　torque　deviation　into　angle　deviation　by　using　a　three-dimensional　characterization　model　of　lost　motion.　Based　on　the　expression　of　TE,　we　proposed　an　evaluation　method　for　the　accuracy　of　the　testing　bench.　Furthermore,　we　presented　the　methods　for　calculating　the　error　sources　and　proposed　a　method　for　determining　the　TE　of　adjacent　units　based　on　the　specific　coupling　structure.　Finally,　we　conducted　practical　tests　to　validate　the　effectiveness　of　the　proposed　method　in　evaluating　the　accuracy　characteristics　of　the　testing　bench.　We　found　that　the　relative　test　error　between　quasi-static　TE　and　dynamic　TE　is　small,　and　more　accurate　test　results　are　obtained　when　applying　an　appropriate　load.