The rearrangement of propylene oxide is greatly affected by the acidity of the catalyst. ZSM-5 zeolite with easily regulated surface acidity was used to catalyze the reaction with propionaldehyde as main product. The difference in the ratio of silica to alumina resulted in significant changes in the acidity. The results show that the ratio of the amount of Lewis acid sites (LAS) to the amount of BrOnsted acid sites (BAS) has a great positive influence on the catalytic performance. When the ratio of silica to alumina reaches 50, the ratio of the LAS to BAS reaches the maximum value of 18.6, the catalytic performance is excellent. The in-situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) was employed to study the adsorption and reaction behavior of propylene oxide on the ZSM-5 catalyst. Results showed that the epoxy ring of propylene oxide first adsorbs on the Lewis acid site (Al atom with empty electron orbital) of ZSM-5 catalyst to form an intermediate with the bond between C=O and C-O which then converts to the propionaldehyde. The Lewis acid sites is of great importance for the reaction. [GRAPHICS]