Photothermal antibacterial material RMG is provided in the present invention, where R represents aldehyde, di-aldehyde or multi-aldehyde, M is magnetic material, and G is reduced graphene oxide. A method of synthesizing the abovementioned antibacterial material comprises of three steps. At first graphene oxide was synthesized, followed by simultaneous reduction and functionalization with MNPs and eventually an aldehyde is modified on magnetic material to yield magnetic G functionalized glutaraldehyde (RMG). We utilize the photothermal feature of graphene for antibacterial activity, in addition graphene was functionalized with aldehyde for capturing bacteria and with magnetic material to enhance a focusing of light irradiation. Moreover, the magnetic properties of material could help for reusability of antibacterial material.