Disclosed is a catalyst for producing ethylbenzene in one-step by vapor phase alkylation reaction of ethanol and benzene. The catalyst has the following features for the reaction: high alkylation reaction activity, high selectivity of ethylbenzene in an alkylation product, high hydrothermal stability and stable catalytic performance. The catalyst comprises a mesoporous-microporous composite TNU-9 molecular sieve and the silicon to aluminum molar ratio, SiO2/Al2O3, of the meso-microporous composite TNU-9 molecular sieve ranges from 50 to 200.