The invention relates to a method for preparing graphene. The method comprises the following steps: (1) adding graphite oxide into water, and performing ultrasonic dispersing treatment to obtain graphene oxide suspension liquid; (2) adding red aluminium into the graphene oxide suspension liquid, and stirring to obtain a mixed solution of the red aluminium and the graphene oxide; (3) filtering themixed solution which is obtained in the step (2), performing microwave heating and activating treatment on filtrate, cooling, performing acid pickling, washing with water, filtering and drying to obtain the graphene. Compared with the prior art, the preparation method provided by the invention is simple and high in efficiency; the obtained graphene is large in specific surface area.