Based　on　the　fuzzy　control　theory,　the　position　and　orientation　control　of　a　4-DOF　planar　underactuated　robot　is　investigated.　The　4-DOF　planar　underactuated　robot　is　a　complex　second　order　non-holonomic　system　with　redundancy　and　underactuation.　Using　the　coupling　effect　between　the　acceleration　of　passive　joint　and　that　of　active　joints,　the　motion　of　the　passive　joint　is　controlled.　The　trajectory　tracking　of　end　point　and　the　orientation　control　of　end　link　of　robot　are　achieved　simultaneously.　A　double　fuzzy-PID　compound　controller　is　designed　for　the　two　subtasks　based　on　the　hierarchical　control　idea.　The　controller　is　verified　by　the　co-simulation　in　Matlab　and　ADAMS.　The　experiment　of　the　position　and　orientation　control　of　the　4-DOF　planar　underactuated　robot　is　realized　on　the　experimental　test　bed　based　on　PMAC　controller.　The　results　of　simulation　and　experiment　indicate　that　the　fuzzy-PID　compound　controller　is　feasible　and　effective　for　the　position　and　orientation　control　of　4R　horizontal　underactuated　robot.　©,　2015,　Journal　of　Mechanical　Engineering.　All　right　reserved.