The LiFePO4/MWCNTs composite used as cathode was synthesized by ball milling. XRD and SEM experiments demonstrated that MWCNTs didn’t change the olivine structure of LiFePO4 and that MWCNTs decentralized into the grains of LiFePO4 and working as electric bridge improving the electrochemical properties of LiFePO4. The electrochemical performance of the composite electrodes with different MWNTs in diameter were studied by button cell. The result indicated that the composite with largest diameter MWNTs exhibited best electrochemical performance. The first charge-discharge specific capacity of the composite with MWNTs of 60-100nm in diameter were 136mAh/g-1 and 129 mAh/g-1 respectively at 0.1C rate under room temperature. The difference between charge-discharge platforms of the composite electrode was the least compared to the others. This phenomenon showed that the material had the largest chemical diffusion coefficient of lithium. At the same time, the capacity of the composite only lost 4.0％ after 10 cycles and kept constant after 20 cycles.