The invention discloses a modified lithium-ion battery cathode material, which comprises a cathode material body and a lithium tungstomolybdic acid layer, wherein the lithium tungstomolybdic acid layer coats the surface of the cathode material body; and the mass ratio of the lithium tungstomolybdic acid layer to the cathode material body is (0.5-5) to 100. A preparation method comprises the following steps: (1) adding a lithium salt and a tungsten-molybdenum source to a solvent, and dissolving the lithium salt and the tungsten-molybdenum source to form a solution; (2) adding the cathode material body to the solution obtained from the step (1), stirring the cathode material evenly at constant temperature and drying the cathode material to obtain a precursor; and (3) heating the precursor to 250-550 DEG C, and roasting and cooling the precursor, so as to obtain the modified lithium-ion battery cathode material. According to the modified lithium-ion battery cathode material disclosed by the invention, the lithium tungstomolybdic acid layer coats the surface of the battery cathode material; CO2, H2O and electrolyte in air can be relatively well isolated; and the air storage performance of the material, the high-temperature electrolyte storage performance and the electrochemical cycling stability of the material are greatly improved.