A preparation method of a composite lithium iron phosphate material relates to a lithium ion battery cathode material. The method comprises the following steps: feeding main raw materials of Fe(NO)3, LiH2PO4, oxide doped with metal ions, and a polymer organic carbon source into an autoclave according to a stoichiometric ratio, adding water and argon to allow the raw materials to react and to be mixed well so as to obtain a slurry; cooling the slurry, drying and sieving; sintering the materials in argon atmosphere to obtain primary sintered materials; sieving the primary sintered materials, continuing to sinter the materials in argon atmosphere, cooling to obtain a composite lithium iron phosphate material. The prepared composite lithium iron phosphate material has high conductivity and excellent electrochemical performance, and the process is stable and simple, is easy for industrial production.