By means of manipulating the oxygen content in graphite oxides (GO) and/or graphene-based materials, we demonstrate that the microwave absorption capacity of carbon materials is highly dependent on their chemical composition and structure. The increase of oxygen in GO remarkably decreases its microwave absorption capacity due to the size decrease of the π–π conjugated structure in these materials, and vice versa. It was revealed that graphene is an excellent microwave absorbent while GO with poor microwave absorption capacity, the unoxidized graphitic region “impurities” in GO act as the microwave absorbents to initiate the microwave-induced deoxygenation. The addition of a small amount graphene to GO leads to avalanche-like deoxygenation reaction of GO under microwave irradiation (MWI) and graphene formation, which was used for electrode materials in supercapacitors. The interaction between microwaves and graphene or graphene-based materials may be used for the fabrication of a variety of graphene-based nanocomposites with exceptional properties and a wealth of practical applications.