The invention relates to a preparation method for generating a phenylethane molecular sieve catalyst by the alkylation of dilute ethylene and benzene as well as the application thereof. The preparation method and the application are characterized in that (I) components of the catalyst: the catalyst comprises one of MCM-22 molecular sieve and MCM-49 molecular sieve or a mixed molecular sieve thereof, aluminum oxide and clay component; (II) preparation steps: (1) an MCM-22 or MCM-49 molecular sieve with silica-aluminum ratio being 25 to 35 is exchanged in ammonium salt with density being 0.5N to 0.8N at 90 DEG C to 100 DEG C, then the mixture is filtered and washed, and drying is carried out at 100 DEG C to 120 DEG C, and the ammonium salt exchange is carried out for a plurality of times; (2) the product obtained from step (1) is kneaded, squeezed and shaped with a binding agent, drying is carried out at 100 DEG C to 120 DEG C and calcination is carried out for 4 hours to 6 hours in flowing atmosphere; (3) the product obtained from step (2) is treated by the ammonium salt with the concentration being 0.6N to 1.0N and organic acid with the weight concentration being 5 percent to 10 percent at 90 DEG C to 100 DEG C for 2 hours to 4 hours, the product obtained is filtered and washed, drying is carried out at 100 DEG C to 120 DEG C, and the treatment of the ammonium salt and the organic acid is carried out for a plurality of times.