Transmission　error　is　the　key　index　for　characterizing　the　transmission　precision　of　precision　reducers,　and　its　accurate　measurement　is　significant　for　the　precision　evaluation　of　precision　reducers.　Transmission　error　is　generally　measured　under　the　conditions　of　zero-load　and　low　speed.　However,　low　speed　is　a　general　concept　and　there　is　no　general　standard　of　measurement　speed　or　solid　scientific　basis.　Therefore,　it　is　difficult　to　obtain　consistent　transmission　precision　evaluation　results　for　the　same　precision　reducer.　The　concept　of　optimal　measurement　speed　in　the　transmission　precision　evaluation　of　precision　reducers　was　put　forward　in　order　to　reduce　the　influence　of　measurement　speed.　The　determination　method　of　optimal　measurement　speed　was　proposed　and　the　calculation　model　of　the　optimal　measurement　speed　was　established,　according　to　the　Stribeck　friction　model　of　precision　reducers.　Taking　a　certain　type　of　RV　reducer　as　an　example,　the　transmission　error　measurement　experiments　were　carried　out　under　different　speeds.　The　friction　torque　of　the　RV　reducer　and　the　peak-to-peak　value　of　the　measured　transmission　error　were　the　least　under　the　optimal　measurement　speed.　The　influence　of　speed　on　the　measurement　results　can　be　effectively　reduced.　The　determination　of　optimal　measurement　speed　of　transmission　errors　could　improve　the　measurement　precision　of　the　transmission　errors　for　the　objective　evaluation　of　transmission　precision　of　precision　reducers.