This present invention discloses a method for preparing graphene, a thin-film transistor, an array substrate, and a display panel. Above all, an amorphous carbon thin film and a catalyst metal thin film are formed on a base substrate in this order. Then, the catalyst metal thin film and the amorphous carbon thin film are allowed to form a eutectic at a high temperature caused by an excimer laser in a manner of excimer laser irradiation. When the irradiation is finished, the surface temperature of the catalyst metal thin film is drastically decreased, allowing most of carbon atoms of the amorphous carbon thin film to be locked in the catalyst metal thin film and only a small amount of carbon atoms to be precipitated on the lower surface of the catalyst metal thin film, so that a graphene thin film is formed. Since the above described the method employs excimer laser irradiation to grow a graphene thin film, and the excimer laser has minor effect on other film layers located under the graphene thin film, graphene can be formed on the base substrate without a transfer process. Therefore, damage and contamination of graphene thin film caused by the transfer process are prevented and properties of graphene thin film are ensured.