The invention relates to a rechargeable magnesium battery cathode material. The percentages by weight of the chemical components of the rechargeable magnesium battery cathode material are: 80 to 90 percent of titanium dioxide, 5 to 10 percent of activated carbon and 5 to 10 percent of carbon nanotubes. A preparation method for the rechargeable magnesium battery cathode material mainly includes the following steps: the powder of three types of elements, i.e. titanium, aluminium and carbon, is sintered by spark plasma, so that Ti3AlC2 is synthesized; Ti3C2Tx is obtained by hydrofluoric acid erosion; Ti3C2Tx is put into glucose or sucrose solution, and activated carbon-coated Ti3C2Tx is obtained by hydrothermal carbonization; aqueous hydrogen peroxide solution is added into activated carbon-coated Ti3C2Tx, and after oxidation in a hydrothermal reaction kettle, activated carbon-coated two-dimensional layered titanium dioxide is obtained; the activated carbon-coated two-dimensional layered titanium dioxide is mixed with the carbon nanotubes, an appropriated amount of deionized water is added, and after stirring and ultrasonic oscillation, the rechargeable magnesium battery cathode material is obtained. The rechargeable magnesium battery cathode material obtained by the invention is nontoxic, harmless, safe and environment-friendly, the structure is novel, and both the cycle performance and rate capability of the magnesium battery are greatly enhanced.