A method for preparing lithium ferrous phosphate using ferrous oxalate comprises the following steps:

1. According to the molecular formula LiFe1-xMxPO4/C, ammonium ferrous sulfate X and (1-x) molar oxalate were weighed. Among them, X was 0-0.01 and M was copper, Co, Ca, Zn, Mg, Ni, Ti, V or Mo. The excessive concentration of oxalic acid solution was 0.1mol/L-0.7mol/L. The oxalate crystals were obtained by heating to 60-90 C and stirring. The oxalate crystals were copper oxalate, cobalt oxalate, calcium oxalate, zinc oxalate and oxalate. Magnesium, nickel oxalate, titanium oxalate, vanadium oxalate or molybdenum oxalate;

2. Ball milling of phosphate, ferrous oxalate crystals, lithium salts and carbon sources respectively. The particle size of phosphate and ferrous oxalate ball milling is 8-20 micron, and that of lithium salts and carbon sources is 2-10 micron. The phosphate is diammonium phosphate, ammonium dihydrogen phosphate or ammonium phosphate. The lithium salts are lithium acetate, lithium carbonate, lithium hydroxide, lithium oxalate or lithium citrate. The carbon source is sucrose. Glucose, fructose, polyisoglycol or acetylene black;

3. The molar ratio of phosphate, ferrous oxalate crystal and lithium salt is 1:1:1. The amount of carbon source is to make the carbon content of the prepared lithium ferrous phosphate cathode material reach 2%-6%.

4. Loading the material weighed in the third step into mixer, after mixing for 2-4 hours, discharging material and putting it into ball mill for ball milling. The ball milling time is 20-30 hours. After ball milling, it dries naturally and passes through 100 mesh sieve. The ball used in ball milling is agate ball with half diameter of 30 and half diameter of 10. The ratio of ball weight to powder weight is 4:1. The ball milling medium is alcohol or acetone, medium weight and powder weight. The ratio of quantity is 1:1.

5. Under the protection of nitrogen, the material prepared in the fourth step is sintered in two stages of low temperature and high temperature. The low temperature section is 200-400 C, the heat preservation period is 5-20 hours, the high temperature section is 600-800 C, the heat preservation period is 10-30 hours, and the heating rate is 0.5 C/min 3 C/min. After cooling to room temperature, the lithium ferrous phosphate is prepared through 300 mesh sieve.