The invention relates to a method for preparing a lithium iron phosphate composite material for lithium cells. The products prepared by the conventional method are undesirable in carbon encapsulation uniformity and purity. The method comprises: firstly, dissolving soluble lithium compound in deionized water to prepare lithium-containing solution in which the lithium ion concentration is 0.3 to 0.9mol/L, adding graphene oxide, stirring, and after the graphene oxide is dispersed, adding phosphoric acid and ferrite to form mixed solution; secondly, filling the mixed solution in a stainless reaction kettle, reacting for 1 to 4 hours at 180 to 220 DEG C, filtering reaction liquid, washing, and drying to obtain a lithium iron phosphate/graphene oxide composite material; and finally, charging hydrogen to perform a reduction reaction to obtain the lithium iron phosphate/graphene oxide composite material. In the lithium iron phosphate/graphene oxide composite nano material obtained by the method, the composition is uniform, the conductivity of lithium iron phosphate is improved greatly, the low conductivity of the lithium iron phosphate cathode material is overcome successfully, and the capacity under large-current discharge of the cells is improved.