The invention discloses a method for preparing ethylbenzene by reaction of dilute ethylene and benzene, which uses the dilute ethylene in dry gas of oil refinery as raw material, water washing and selective removal of propylene are conducted for the dry gas before the dry gas enters an alkylation reactor in sections, alkylation reaction of the dilute ethylene in dry gas and the benzene proceeds under the circumstances that zeolite catalyst exists, the dry gas and / or low-temperature gas-phase benzene are utilized for taking heat during the alkylation reaction, and the reaction temperature rising is reduced; after the vapor-liquid separation of the alkylation reaction product, tail gas is discharged from the device through low-temperature absorption, and cycle benzene, ethylbenzene, propyl benzene, diethylbenzene and heavy component are sequentially separated from the liquid product through a separation system; the diethylbenzene and the benzene are mixed and enter an anti-alkylation reactor and anti-alkylation reaction proceeds on molecular sieve catalyst for further converting to the ethylbenzene. The invention effectively reduces the benzene consumption and the energy consumption during the course of preparing ethylbenzene by dilute ethylene, the ethylene conversion rate is more than or equal to 99%, the total selectivity of generating ethylbenzene is more than or equal to 99%, the recovery rate of benzene carried by the tail gas is more than or equal to 99.5%, and the xylene content in the ethylbenzene is less than 800 ppm.