The invention relates to a 6,7-dihydro-5H-diphenyl[a,c]cyclohepta-5-ketone compound and a preparation method thereof. A formula of the compound is as shown in the specification. O-bromoaryl methanol, aryl ethanone, [Ir(cod)Cl]2, a palladium salt, a sliver salt, 1,1'-binaphthyl-2,2'-bisdiphenylphosphine and alkaline are taken and added into an organic solvent, heated and refluxed in the presence of an N2 gas, filtered, evaporated and re-crystallized after the reaction is ended to obtain the 6,7-dihydro-5H-diphenyl[a,c]cyclohepta-5-ketone compound. The 6,7-dihydro-5H-diphenyl[a,c]cyclohepta-5-ketone compound is synthesized by one step, wherein the reaction substrate scope is wide, the yield is high, the reaction is economical and efficient, and the application prospect is wide.