Abstract: To investigate the catalytic properties of β zeolite for catalytic alkylation of C₉ aromatics with propylene, β zeolites modified with phosphorus were prepared by using impregnation method. The modified β catalysts with different loading amount of phosphorus were characterized by XRD, SEM, EDX, MAS NMR, Py-IR, N₂ adsorption-desorption, and NH₃-TPD. The results showed that the morphology and crystal structure of the β zeolite catalysts did not change obviously after modification with phosphorus. However, the specific surface area and the surface Si/Al mass ratio of the β zeolite decreased with the increase of amount of phosphorus. It was proved that the interaction between the phosphorus and β zeolite could affect the acid strength distribution of β zeolite and the catalytic performance of alkylation of C₉ aromatics. In comparison with β zeolite, the β zeolite modified with 0.5% phosphorus (β-0.5P) had good catalytic performance in alkylation reaction of C₉ aromatics. The ratio of C₁₂₊ aromatics in the alkylation products was up to 17%, and the value of m_1,3,5-TMB/m_C9 was increased by 5.3%. The β-0.5P catalytic activity showed stable after reaction for 10 h. However, when the loading amount of phosphorus on β zeolite was too high, the alkylation activity of the catalyst decreased and the isomerization and disproportionation performance of the catalyst increased.