Isokinetic　muscle　strength　training　refers　to　the　mode　of　movement　based　on　constant　speed　and　variable　resistance,　which　can　guarantee　the　maximum　resistance　and　force-distance　output　of　each　muscle　in　different　angles　of　exercise.　In　this　article,　we　develop　an　isokinetic　muscle　strength　training　strategy　based　on　the　adaptive　gain　and　cascade　proportion　integration　differentiation　(PID)　controller　for　ankle　rehabilitation　on　our　newly　developed　ankle　robotic　system.　First,　a　heuristic　threshold　intention　recognition　method　based　on　time-series　integration　was　proposed　to　precisely　recognize　the　motion　intention,　thus　inducing　the　motion　in　this　direction.　Then,　an　adaptive　gain　algorithm　was　developed　to　provide　speed　gain　for　the　isokinetic　training,　to　avoid　jitter　during　speed　switching.　Finally,　the　isokinetic　characteristic　was　realized　by　the　cascade　PID　controller,　which　can　control　the　motion　velocity　in　a　given　range　with　fast　response　speed.　Experiments　with　healthy　subjects　showed　good　performance　in　the　smoothness　of　the　control　system,　the　accuracy,　and　the　real-time　performance　of　velocity　tracking.　By　introducing　the　isokinetic　characteristic　in　ankle　rehabilitation,　the　ankle　robot　can　provide　resistance　training　at　a　constant　speed　no　matter　how　much　force　the　patient　uses,　which　is　a　very　functional　supplement　and　improvement　for　ankle　rehabilitation.