The invention provides a preparation method of a foldable graphene thin film of large area, and belongs to the field of thin film material preparation technology. The method comprises the following steps: firstly, oxidized graphene suspension liquid is prepared; a reducing agent is added into the oxidized graphene suspension liquid, in order to obtain mixed liquor of oxidized graphene and the reducing agent; finally the mixed liquor is uniformly applied on a substrate, heating is carried out for forming the film, reduction is carried out, and the graphene thin film is obtained. Two traditional independent steps including film formation and reduction are realized by one step, heating is carried out for forming the film and reducing oxidized graphene simultaneously, so that the preparation process of the graphene thin film is simplified; when the coated substrate is heated, the reducing agent is dissipated from the inner side of oxidized graphene, so that the reduction process for oxidized graphene is formed from the inner side to the outer side, and the problem of incomplete reduction of oxidized graphene is effectively solved; at the same time, dissipation of the reducing agent enlarges the specific surface area in the thin film, a loosened multilayer structure is formed in the graphene thin film, agglomeration phenomenon of graphene is reduced, and quality of the graphene thin film is improved.