Lithium iron phosphate (LiFePO₄) was prepared by hydrothermal synthesis using LiOH·H₂O, FeSO₄·7H₂O and H₃PO₄ as raw materials. We report the effects of pH, reaction temperature and reaction time on the structure properties including crystallite size, lattice parameters, and (020) crystallographic direction of LiFePO₄ particles by X-ray diffraction (XRD) method. The chemical process of the precipitation from Li–Fe(II)–P–H₂O system was also investigated. We present the evolution of the product by a solubilization-reprecipitation mechanism based on the difference of solubility products (K_sp) of different precipitates. It provides an effective and reasonable way to prepare nano-LiFePO₄ with excellent structure properties.