The electrochemical performance of lithium iron silicate (Li₂FeSiO₄) as a cathode material for lithium ion batteries would be remarkably enhanced by selective substitution of 25% oxygen with 25% sulfur to form a Li₂FeSiO₃S compound based on the previous first-principles calculation. However, the experimental verification has little studied. In this work, the sol-gel precursor and solid-state reaction route was employed to prepare a series of carbon coated Li₂FeSiO₄ (Li₂FeSiO₄/C) composites with different sulfur modifications using 1-dodecanethiol as a sulfur source material. The effects of important preparation parameters including sucrose amount, sulfur content, sintering temperature and sintering time on the crystal structure, surface morphology and electrochemical performance of sulfur modified Li₂FeSiO₄/C composites were investigated through orthogonal design experiments. The results indicated that the significance of the influence on the capacity performance in decreasing order followed sulfur doping content > carbon content > sintering temperature > sintering time. The optimized synthesis conditions were determined to be carbon content of 50% and sulfur doping content of 20% with the sintering temperature at 650°C for 12 h.