The　energy　of　the　exhausted　high-pressure　air　from　a　proton　exchange　membrane　(PEM)　fuel　cell　can　still　be　recovered.　The　performance　of　the　scroll　expander　used　for　recovering　this　energy　is　studied　in　this　paper.　A　numerical　simulation　of　the　expander　is　presented,　and　then　the　simulated　results　are　compared　with　that　of　the　experiment　results　gleaned　from　the　prototype　of　the　expander.　The　matching　of　the　flows　and　pressure　characteristics　between　the　compressor-expander　(C-E)　is　also　discussed.　Finally,　this　paper　points　out　that　leakage　has　a　significant　effect　on　the　volumetric　efficiency,　the　quantity　of　recovered　work,　and　other　performance　indicators　of　the　scroll　expander.　The　matching　of　the　C-E　is　a　key　factor　in　the　practical　application　of　this　system.