The　development　of　robotic　hand　that　can　imitate　human　movements　has　always　been　an　important　research　topic.　In　this　paper,　a　linkage-driven　underactuated　three-finger　hand　is　proposed　to　imitate　the　flexion/extension　(f/e)　and　abduction/adduction　(a/a)　motions　of　human　hand.　The　robotic　hand　has　three　identical　underactuated　fingers,　each　of　which　contains　an　underactuated　planar　linkage,　a　spherical　four-bar　mechanism,　and　a　set　of　bevel　gears.　The　spherical　four-bar　mechanism　is　designed　to　provide　2-degree-of-freedom　actuation,　driving　the　f/e　and　a/a　motions　of　the　proximal　joint　simultaneously.　Based　on　screw　theory,　the　kinematic　model　of　the　spherical　mechanism　is　established,　and　the　maximum　available　workspace　index　(MAW)　of　the　spherical　mechanism　is　proposed　to　evaluate　the　workspace　with　the　same　adduction　and　abduction　angle　ranges.　The　effects　of　the　parameters　of　the　spherical　mechanism　on　the　MAW　and　the　transmission　efficiency　are　obtained,　and　the　parameters　of　the　spherical　mechanism　are　optimized.　The　optimization　results　show　that　the　MAW　of　the　spherical　mechanism　can　be　increased　by　up　to　3.5　times.　Finally,　experiments　are　carried　out　to　show　the　proposed　robotic　hand　can　perform　simultaneous　adaptive　grasping　and　in-hand　manipulation.　Note　to　Practitioners-The　robotic　hand　is　of　great　significance　for　replacing　workers　in　heavy,　repetitive,　and　unsafe　working　environments.　Uncertain　environments　in　non-manufacturing　fields,　such　as　industries　for　pick-and-place,　sorting,　palletizing,　assembly　and　other　operations,　marine　development,　and　medical　service,　require　that　robotic　hands　can　operate　tasks　like　human　hands.　Inspired　by　the　human　hand　with　the　f/e　and　a/a　motions,　a　linkage-driven　underactuated　three-finger　hand　is　proposed　in　this　paper　to　imitate　the　functions　of　the　human　hand.　Due　to　its　underactuated　characteristics　and　a/a　function,　the　designed　robotic　hand　is　more　dexterous　and　economical.　The　effects　of　the　design　parameters　of　the　spherical　mechanism　on　the　MAW　and　the　transmission　efficiency　are　analyzed,　and　the　parameters　of　the　spherical　mechanism　are　optimized　to　improve　the　performance　of　the　robotic　hand.　This　approach　can　be　used　in　other　industrial　applications　related　to　the　robotic　hand　or　the　spherical　mechanism.