Highly energy density olivine LiMn0.7Fe0.3PO4/C composite was synthesized by coprecipitation method followed by ball milling. The composite was characterized by elemental analysis, XRD, SEM, TEM and its electrochemical property was also studied. This electrode presents an enhanced electrochemical intercalation performance of lithium ions, a narrow particle size distribution, and an excellent electrochemical performance. Especially, the coprecipitation method reduces Mn dissolution into the electrolyte, a common problem in LiMnPO4 which influence its energy density, due to the homogeneous distribution of transition metals. The electrochemical performance of LiMn0.7Fe0.3PO4/C and the Mn dissolution rate with long term cycles were investigated by CV and EIS to further understand the intrinsic properties of the high Mn content LiMn0.7Fe0.3PO4/C materials. Our results indicate that homogeneous distribution of Mn and Fe is very important to achieve a higher energy density.