The invention discloses a preparation method of carbon-doped lithium iron phosphate. The preparation method comprises the steps of stirring and mixing dialkyl phosphate and lithium hydroxide, and allowing to stand to obtain a first organic phase and a first water phase; separating the first organic phase from the first water phase, placing the first organic phase in a sealed reaction kettle, introducing nitrogen, adding ferrocene and butyl titanate in a mixed way, and performing uniform mixing and stirring to obtain a mixed organic matter; and adding the mixed organic matter into a boiling furnace in a spraying mode, adding air, introducing sulfur dioxide gas, continuing to react for 2-3 hours, introducing nitrogen for 30-60 minutes, and cooling and collecting the material, thereby obtaining the carbon-doped lithium iron phosphate. The preparation method is simple in process and low in cost, and the obtained carbon-doped lithium iron phosphate is uniformly doped in lithium iron phosphate and has the advantages of better conductivity, high compaction density and tap density, short flow, small sewage production quantity and low cost.