The optimal experimental conditions (sintering time is 4 h, the sintering temperature is 650 °C, and the mass percentage of citric acid and pickled iron oxide red is 80.25%) for the synthesis of LFP/C cathode materials were determined by orthogonal experiments. To further improve electrochemical performance, Cl-doped LiFePO4/C cathode material was successfully synthesized by high-temperature solid phase method using pickling iron oxide red and citric acid as the iron source and carbon source, respectively. The experimental results reveal that it is a practical method to prepare LiFePO4/C cathode material by pickling iron oxide red as raw material to reduce production cost. It is also proved that Cl doping can effectively change the microstructure, improve the structural stability and improve its rate performance, cycle performance and ion diffusion rate of LiFePO4. The initial capacity of Cl-doped LiFePO4/C electrode achieves 164.1 mAh g− 1 at 0.1C, which is about 96.53% of the theoretical capacity (170 mAh g− 1). The Cl-doped LiFePO4/C electrode material can achieve the reversible capacity of 105.3 mAh g− 1 with the capacity retention rate of 91.5% after 500 cycles at 10C, which is much higher than that of undoped LiFePO4/C (62.7%) electrode materials.