Spray drying and carbothermal method was employed to investigate reaction mechanism and electrochemical performance of LiFePO4/C cathode by using different carbon sources. Micro-structural variations of LiFePO4/C precursors using different carbon sources were studied by Thermo-gravimetric (TG)/Differential Thermal Analysis (DTA). The LiFePO4/C samples were characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) absorption spectroscopy. The results indicated that the crystallization temperature of LiFePO4 was 453°C, while the transform temperature was 539°C from Li3Fe2(PO4)3 to LiFePO4. At 840°C, LiFePO4/C sample with an excess of impurity phase Fe2P gave much poorer electrochemical performance. The severe decomposition of LiFePO4/C happened at 938°C and generated impurity phases Li4P2O7 and Fe2P. The clear discharge platform of Fe2P emerged at around 2.2V.