The invention relates to a method for preparing graphene, belonging to the technical field of materials. The method comprises the steps of: mixing natural flake graphite powder and ionic liquid; carrying out mechanical grinding under the anaerobic condition; then dispersing the obtained mixture in water; carrying out centrifugation to remove by-product; and volatilizing solvent (water) to obtain the graphene which is in an ionic liquid binding state. The method is low in raw material cost, simple in operation, high in efficiency, energy-saving and environment-friendly; and the graphene which is in the ionic liquid binding state and is prepared by the invention has the layer numbers within the range of 1-10, and does not contain oxidation group, so that excellent electric conduction and electrochemical catalytic activity are maintained, and the graphene is especially suitable for preparing a high-performance electrode.