Abstract: LiFePO₄/C doped by Mg ion was obtained by solid phase reaction synthesis route with PVA (polyvinyl alcohol) coating processing. Conduction properties at different temperatures and resistivity change at different dopant contents indicate that conduction mechanism of LiFePO₄ will change from n type to p type along with the increasing of doping content. Crystallization of LiFePO₄/C with the dopant content of 0.3％(x) at different synthesis temperatures was characterized. For the sample synthesized at 973 K, the particles with a diameter of several hundred nanometers together with carbon decomposed by PVA formed secondary particles with a diameter of 10 micrometer. Along with curves of cyclic voltammetry, two shoulder-peaks showed that another way for lithium ion extraction/ insertion in cathode existed. When batteries were cycled at a rate of 0.1 C, the charge and discharge curves showed flat work voltages and large capacities. When the charge-discharge rate was increased to 0.5 C, LiFePO₄ covered by carbon and doped by Mg ion showed capacity of more than 120 mA•h•g^－1. After 100 cycles, the capacity fade was neglectable.