Abstract: Phosphorus modified β zeolite samples were prepared by using ammonium biphosphate solution under high temperature and pressure. The crystallinity, elemental composition, acidity and structure of the phosphorus modified β zeolite samples were characterized, and their catalytic activities during benzene-ethylene alkylation under high space velocities were investigated. Results showed that the total acid amount, B-acid sites and L-acid sites of the P-modified β zeolite samples increased significantly. Furthermore, structures of P(4Al) and Al(4P) were found existing in the framework of P-modified β zeolite as shown by 31P MASNMR and 27Al MASNMR spectrum, thus, the framework aluminum atoms were stabilized and the activity stability of the zeolite catalyst enhanced. P-modified β zeolite catalyst with 2% P2O5 exhibited the best activity stability during benzene-ethylene alkylation under high space velocity.