In　order　to　improve　the　response　speed　and　disturbance　rejection　ability　of　a　permanent　magnet　synchronous　motor　(PMSM)　in　an　electromechanical　actuator　(EMA),　a　compound　sliding　mode　control　(CSMC)　is　proposed.　The　CSMC　consists　of　a　sliding　mode　controller　with　a　new　reaching　law　and　disturbance　observer　based　on　a　symmetric　S-type　function.　The　stability　of　the　CSMC　is　analyzed　using　the　Lyapunov　stability　analysis.　The　effectiveness　of　the　CSMC　is　confirmed　by　the　Simulink　simulation,　and　experiments　were　conducted　on　a　semi-physical　platform.　The　results　obtained　by　comparing　the　CSMC　with　the　proportional　integral　(PI)　control　and　traditional　sliding　mode　control　show　that　the　CSMC　has　a　faster　response　and　stronger　disturbance　rejection　ability　and　reduces　chattering.