The　dynamic　characteristics　of　lost　motion　based　on　transmission　errors　were　explored.　By　considering　the　influences　of　torque,　loading　rate,　and　rotational　speed,　the　relationship　between　lost　motion　and　transmission　errors　was　analytically　derived.　The　dynamic　characteristics　of　lost　motion　were　substantiated,　revealing　that　lost　motion　can　be　obtained　by　subtracting　reverse　transmission　errors.　The　classification　of　lost　motion　was　examined,　and　lost　motion　was　divided　into　dynamic　lost　motion,　quasi-static　lost　motion,　and　static　lost　motion.　The　testing　methods　for　lost　motion　were　provided,　by　which　dynamic　lost　motion　can　be　obtained　through　bidirectional　transmission　error　analysis,　and　quasi-static　lost　motion　and　static　lost　motion　can　be　acquired　through　hysteresis　loop　analysis.　Experimental　investigations　on　lost　motion　were　conducted　using　examples　of　small　and　large　reducers,　confirming　the　dynamic　characteristics　of　lost　motion.　It　was　observed　that　dynamic　lost　motion　and　quasi-static　lost　motion　exhibited　dynamic　variations,　while　static　lost　motion　was　kept　unaffected　by　loading　rate　dependence,　aligning　with　theoretical　analyses.　In　conclusion,　the　theoretical　and　engineering　values　of　the　research　were　highlighted.　©　2024　Beijing　University　of　Aeronautics　and　Astronautics　(BUAA).　All　rights　reserved.