The invention discloses a mixed positive electrode material and application thereof, belonging to the technical field of energy materials. According to the invention, lithium manganate and lithium manganese iron phosphate are both used as positive electrode active materials, so good safety performance and cycle performance of a lithium manganese iron phosphate material and high energy density and good processing performance of a lithium manganate material are utilized. Compared with a battery prepared from lithium manganate or lithium manganese iron phosphate, a battery prepared from the positive electrode material provided by the invention has the following characteristics: (1) high volume energy density, wherein the mixed positive electrode material has compacted density of 2.6 to 2.8 kg/m3 and volume energy density of more than 300 Wh/L; (2) good cycle performance, especially at high temperature; (3) excellent safety performance, which enables the disadvantage of poor security of traditional lithium manganate to be overcome; and (4) good processing performance, wherein the mixed positive electrode material can effectively improve problems of low adhesion of pole pieces, difficult processing, etc. due to a great specific surface area of the lithium manganese iron phosphate material and enables production process to be greatly simplified.