Small crystallites LiFePO4 powder with conducting carbon coating can be synthesized by ultrasonic spray pyrolysis. Cheaper trivalent iron ion is used as the precursor. The pure olivine phase can be prepared with the duplex process of spray pyrolysis (synthesized at 450, 550 or 650°C) and subsequent heat-treatment (at 650°C for 4h). The results indicate that the pyrolysis temperature of 450°C is appropriate for best results. The carbon coating on the LiFePO4 surface is critical to the electrochemical performance of LiFePO4 cathode materials of the lithium secondary battery, since the carbon coating does not only increase the electronic conductivity via carbon on the surface of particles, but also enhance the ion mobility of lithium ion due to prohibiting the grain growth during post-heat-treatment. The carbon of 15wt.% evenly distributed on the final LiFePO4 powders can get the highest initial discharge capacity of 150mAhg−1 at C/10 and 50°C.