The present invention discloses a process for preparing perhydrofluorene or alkyl-substituted perhydrofluorene, comprising the steps of: (1) reacting a phenolic compound or an aromatic hydrocarbon compound or an aromatic ketone compound or an aromatic ether compound with a benzyl compound to carry out an alkylation reaction in the presence of a first catalyst, thereby to produce substituted or unsubstituted diphenyl methane, wherein the first catalyst is an acidic catalyst; and (2) reacting the substituted or unsubstituted diphenyl methane with hydrogen gas to carry out an hydrogenation reaction or a hydrodeoxygenation reaction, thereby to produce perhydrofluorene or alkyl-substituted perhydrofluorene, wherein the second catalyst is a physical mixture of a metal catalyst and an acidic catalyst or a metal catalyst loaded on an acidic catalyst.