The invention relates to a method for preparing graphene. The method comprises the following steps: (1) mixing graphite powder and lithium chloride, heating for 1 to 3 hours at 100 to 200 DEG C underthe protection of inert gas, and then cooling to 5 to 10 DEG C; (2) then adding alkyl compounds, and stirring for 1 to 5 hours at 30 to 50 DEG C to obtain an intercalated mixture; (3) heating the intercalated mixture by adopting microwave radiation to damage the interlayer structure of the graphite powder and increase the interlayer space, and finally, peeling by utilizing mechanical shearing equipment to obtain the graphene. Compared with the prior art, the method for preparing the graphene is simple in operation process and easy to control, does not cause pollution to the environment, and issuitable for large-scale preparation on the market.