The invention discloses a preparation method of 1,1-diphenyl ethane. The method includes the following steps: a, mixing styrene and an alcohol accelerator at room temperature, introducing dry hydrogen chloride gas into the mixture; after the reaction, conducting washing and vacuum distillation to obtain an intermediate 2-chloro-2-ethyl benzene; and b, conducting an alkylation reaction on 2-chloro-2-ethyl benzene and benzene by using Lewis acid or an ionic liquid as a catalyst at 0-80 DEG C for synthesizing 1,1-diphenyl ethane. The invention has the beneficial effect that: compared with traditional methods, the two-step synthesis method of 1,1-diphenyl ethane by using styrene as the raw material has rich sources of raw materials, high product yield, repeated use of the catalyst and good environmental protection performance.