Li3V2(PO4)3/C composites (LVP/C) are synthesized by rheological phase reaction (RPR) method using alginic acid (HAlg) as the carbon source. Different process media are applied in the synthetic process to assess the possible effects on LVP/C composite. And the whole synthetic route is discussed in detail with qualitative and instrumental analysis, in terms of ball-milling process, rheology phase reaction process and thermogravimetric analysis of precursors. The much different morphological properties of as-prepared LVP/C composites demonstrate that process medium indeed has some effects on the synthetic process, especially on the refinement and dispersion of particles. According to these investigations, ethylene glycol (EG) is revealed more proper for preparing LVP/C using this method attributed to its moderate viscosity, surface activity and synergistic effects with HAlg. The corresponding LVP/C composite shows nanoscaled particles with smooth surfaces and uniform size distribution. Besides, LVP-EG sample exhibits excellent electrochemical performances under different voltage windows as well. Between 3.0 and 4.3 V, when charge/discharge at 20/50 C, the composite exhibits relatively high capacity and stable cycling performance for 300 cycles. Within 3.0–4.8 V, it can cycle for 200 times at a high rate of 20 C without obvious capacity fading. The outstanding performances can be attributed to the enhanced electronic/ionic conductivities of LVP/C benefitting from the influences of EG and HAlg via the RPR method.