To overcome the problems faced by the preparation of high-performance LiFe0.5Mn0.5PO4/C cathode material for commercial application in large scale, such as complicated procedures in the synthesis process and/or low volumetric energy density of nanometer-sized sample, herein, micro-agglomerated LiFe0.5Mn0.5PO4/C is prepared by a facile surfactant-assisted solid-state route. A composite carbon source and controllable pre-calcining process are used for achieving the homogenous carbon coating, interconnected pores and uniform particle size distribution. X-ray powder diffraction, Raman spectrum, N2-adsorpotion-desorpotion, scanning/transmission electron microscopy and elemental analysis confirm the microstructure and accurate composition of the as-prepared samples. It is found that the composite source not only increases the homogeneity of the carbon coating layer and the pore-forming ability, but also contributes to inhibiting the size growth of the primary particles. Meanwhile, the suitable pre-calcining time can improve the specific surface area and optimize the carbon content and pore structure, and thus enhance the tap density of the as-prepared material. The typical LiFe0.5Mn0.5PO4/C sample with carbon content of 3.50 wt% displays high reversible capacities and good rate capability, with discharge capacities of 155.0, 141.5 and 120.1 mA h g−1 at 0.1, 1.0 and 5.0 C (1 C = 170 mA g−1), respectively. Furthermore, the sample exhibits superior cycling performance, with a capacity retention above 98% after 200 cycles at 1.0 and 5.0 C. As a result, this LiFe0.5Mn0.5PO4/C exhibits great potential as a cathode material for high power/energy lithium ion batteries because of its easy synthesis, high specific capacity, good rate capability and cycle stability.