The invention provides a system and a method for preparing benzene from biomass and acetylene. The system comprises a rotary bed pyrolysis reactor, an acetylene storing device, a cooling device and a benzene separating device. The rotary bed pyrolysis reactor comprises a feed zone, a preheating zone, a reaction zone and a discharge zone, a feed inlet is formed in the feed zone, an acetylene inlet and a pyrolysis oil and gas outlet are formed in the reaction zone, and a discharge outlet is formed in the discharge zone; an acetylene outlet is formed in the acetylene storing device and is connected with the acetylene inlet; a pyrolysis oil and gas inlet and a biological oil outlet are formed in the cooling device, and the pyrolysis oil and gas inlet is connected with the pyrolysis oil and gas outlet; a biological oil inlet and a benzene outlet are formed in the benzene separating device, and the biological oil inlet is connected with the biological oil outlet. The system and the method have the advantages of low investment, simple technological processes, good economic benefits and the like.