High temperature solid phase reaction method was used to synthesize the positive Li₂Fe_1-x-yMn_xNi_ySiO₄/C composites of Li ion battery. The methods of X-ray diffraction (XRD), scanning electron microscope (SEM) and electrochemical analysis method were applied to investigat the effect of Ni & Mn co-doping and C co-modification on the composite structure and properties. The results indicated that co- modification did not change the the crystal structure of Li₂FeSiO₄, Ni and Mn co-doping and C-covering improved the specific capacity and cycling performance of the material, and with C/32 rate charging and discharging, the co-doping Li₂Fe_0.6Mn_0.2Ni_0.2SiO₄/C exhibits the best electrochemical performance. According to the measured result, the initial discharge capacity of the composites is 149 mAh·g-1, its capacity retention ratio is still 95.3% after 10 cycles.