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.