The alkylation of benzene with propylene over Hp zeolite catalyst was studied by means of in situ FTIR and coke characterization. After the catalyst has been impregnated with benzene, propylene can replace adsorbed benzene and react with benzene. In the absence of excess benzene, adsorbed propylene will react with itself. Therefore, a higher molar ratio of benzene to propylene is indispensable. In addition, at higher temperature, propylene can more easily replace adsorbed benzene, so the reaction proceeds more quickly. For the process carried out in a fixed-bed bubble reactor where catalysts are impregnated in the bulk liquid of benzene, propylene oligomerization is suppressed. The coke deposited on the catalyst is composed of multi-substituent aromatic compounds which have single or double rings. The deactivation is caused from pore blockage of bulkier molecules formed by multi-alkylation instead of propylene oligomerization. With the increase of reaction temperature, the decomposition rate of products increases.. The decomposition will form propylene and bulkier molecules, which will block the micropore channel of the catalyst and deactivate the catalyst. At higher temperature, however, bulkier molecules diffuse more quickly; this can prolong the lifetime of catalyst, so the reaction temperature could be too low. The suitable temperature should be 120-166degreesC.