In this work, LiFe1-xMnxPO4@C (x = 0, 0.01, 0.02, 0.03) cathode materials were obtained by a simple co-precipitation method and heat treatment, and the influence of Mn-doped modification on the electrochemical performance of LiFePO4@C cathode materials was investigated. Results show that by doping an appropriate amount of Mn, the cell volume became larger, and the electronic conductivity increased, which improved the Li+ diffusion rate and thus its rate capability and cycle performance of Li-ion batteries. Among them, LiFe0.98Mn0.02PO4@C showed superior lithium storage capability; the discharge capacity can reach 150.7 mAh g−1 at 0.1 C. The cell could discharge up to 155.9 mAh g−1 at 1 C under high temperature at 45 °C, which was higher than LiFePO4@C (142 mAh g−1) under the same test conditions. The discharge capacity of 1 C at room temperature was 139.9 mAh g−1, and the cycle stability was 95.9% after 200 cycles. It showed that it had good rate capability and excellent cycle performance. These results indicate that Mn-doped LFP is a simple and effective strategy for developing high-performance cathode materials.