Exploring a high-efficiency catalyst for the coupling reaction of carbon dioxide (CO2) with epoxide (PO) is still a challenging project. Ionic liquid (IL) is one of the most ideal catalysts since it could catalyze the coupling reaction in a benign environment in the absence of metal and organic solvent. The catalytic activity of a series of pyridinium-based ILs is theoretically investigated. The influences of the nature of cation, methylene chain length, and anion on the catalytic performance are explored. It has been proven that the catalytic activity of pyridinium-based IL is better than that of imidazolium-based and quaternary ammonium-based us. Since the properties of IL could be regulated by variation of cation and anion, four new ILs are designed by introduction of the -COOH, -OH, -SO3H, and -NH2 functional groups into the traditional pyridinium-based IL, respectively. Subsequently, the catalytic performance of four newly designed functionalized pyridinium-based ILs is compared with that of the traditional pyridinium-based IL. Only the carboxyl-functionalized pyridinium-based IL has better catalytic activity than the traditional pyridinium-based IL. It is expected that the theoretical investigation might provide helpful clues for further experiments.