This　paper　addresses　the　problems　of　uncertainties　in　practical　permanent　magnet　synchronous　motors(PMSM)　and　the　inexactly　decoupling　of　passivity-based　controller　(PBC),　and　proposes　an　exactly　decoupled　robust　passivity-based　current　control　strategy　based　on　observer　as　a　solution.　The　passivity-based　controller　is　designed　by　using　the　energy　shaping　and　damping　injection　method　based　on　a　three-phase　PMSM　Euler-Lagrange(EL)model　with　uncertainties.　This　controller,however,　cannot　restrain　the　fluctuations　when　parameters　variations　occur　in　the　actual　system　and　have　a　poor　decoupling　characteristic.　To　overcome　these　problems,　a　new　Luenberger　observer　is　designed　for　the　approximately　decoupled　PMSM　model　to　observe　the　uncertainties　caused　by　parameter　variations,　and　the　errors　caused　by　imperfectly　compensation　of　passivity-based　controller　to　the　coupling　voltage　and　back-electromotive　force　(EMF).　The　output　of　the　observer　will　be　used　for　the　calculation　of　the　reference　voltages　by　a　feedforward　control.　Simulation　has　proved　that　the　new　observer　is　superior　to　conventional　observer.　The　effect　of　coupling　caused　by　imperfectly　compensation　has　been　eliminated,　and　the　exactly　decoupled　robust　control　of　current　loop　has　been　achieved.