The invention provides a lithium iron phosphate battery with high specific property and a preparation method of the lithium iron phosphate battery. The lithium iron phosphate battery comprises a positive plate, a negative plate, a diaphragm, a power type electrolyte, a pole and a battery case, wherein the positive plate adopts an aluminum foil current collector, an integrally formed lug is arranged on one side, a carbon black or carbon nano tube conductive coating is pre-coated on two side surfaces, and then a positive material is coated; the positive material comprises a positive active material, a positive binder and a conductive agent; the positive active material is lithium iron phosphate; the negative plate adopts a copper foil current collector, an integrally formed lug is arranged on one side, a negative material is coated on two side surfaces, and the negative material comprises a negative active material, a negative binder and a conductive agent; the positive lug and the negative lug adopt multi-lug structures respectively, all homopolar lugs are directly divided into two bundles or divided into two bundles after being connected to strip lugs, the lugs are connected with the pole through electron beams or laser melting welding on opposite welding surfaces on two sides of the pole respectively, a sandwich structure is formed, and finally the lithium iron phosphate battery with high specific property is obtained.