A method for manufacturing graphene is provided, comprising (1) introducing a supporting substrate in a reactor; (2) preparing (nano) crystalline alumina catalyst having catalytic activity on the supporting substrate to prepare an insulating substrate; (3) growing nano graphenes on the insulating substrate to manufacture graphene film comprising graphene layer of the nano graphenes, which are grown without use of metal catalyst substantially. The graphene layer composed of the nano graphene has spatially homogeneous structural and electrical properties even in synthesis as large area and can be applied to flexible electronic devices.In addition, as it has easy detachment of the substrate and the graphene film and can detach the graphene film without damage of the substrate, leaving no residual graphene on the substrate, it is possible to grow the nano graphene by reusing the substrate.