This　paper　presents　the　input　coupling　modeling　method　for　a　three-PRR　flexure-based　compliant　stage.　The　input　coupling　modeling　for　planar　compliant　mechanisms　is　first　established.　The　kinematic　structure　of　a　three-PRR　compliant　stage　is　then　designed,　and　its　input　coupling　is　derived　by　using　the　proposed　method.　Subsequently,　the　validation　and　analysis　are　carried　out　by　using　finite　element　method　(FEM).　The　relationships　between　two　main　parameters　and　the　input　coupling　rate　of　the　three-PRR　compliant　stage　are　discussed,　and　the　decoupling　region　is　then　determined.　Finally,　its　geometrical　parameters　are　optimized,　and　the　workspace　calculated　by　the　analytical　method　is　compared　with　that　obtained　from　FEM.　It　not　only　provides　a　new　input　coupling　modeling　method　for　flexure-based　compliant　mechanisms,　but　also　provides　a　reference　for　the　design　of　three-PRR　mechanisms.