The invention relates to a method for preparing a lithium iron phosphate-lithium vanadium phosphate cathode material of a lithium ion battery, which comprises the following steps of: adding ferrous sulfate solution and ammonium metavanadate solution into a stirring reaction kettle, and reacting for 0.5 to 8 hours; adding sufficient hydrogen peroxide into solution, reacting for 0.2 to 0.5 hour, ageing for 2 to 4 hours, filtering, washing, and drying to obtain FeVO4.xH2O powder with high activity; performing heat treatment on the FeVO4.xH2O powder at the temperature of 500 DEG C to obtain pure-phase FeVO4; and performing mechanical activation on the pure-phase FeVO4, a lithium source compound, a phosphorus source compound, a composite carbon source and a composite metal compound serving as raw materials by using water as a medium in the molar ratio of the iron element to the vanadium element to the phosphorus element to the lithium element to the carbon element to the composite metal element of 1:1:2.5:2.5:(0.1-10):(0.01-1), performing spray drying to obtain a lithium iron phosphate-lithium vanadium phosphate composite material precursor containing the composite carbon source and the composite metal element, and roasting in certain atmosphere at the temperature of between 600 and 900 DEG C for 4 to 20 hours to obtain the lithium iron phosphate-lithium vanadium phosphate composite cathode material with high performance.