Abstract: The present disclosure provides a carbon-encapsulated lithium manganese iron phosphate material having a composition of: LiFe1-x-yMnxMyPO4@C, where M includes at least one of Mg, V, Zr, Nb, In, Al, Co and Ni, 0.5?x?0.8, 0<y?0.02, and C is encapsulated carbon. The material has a secondary gradation structure with tightly bound material gradation, high compaction density, and excellent electrochemical performance. The present disclosure further provides a method for preparing a carbon-encapsulated lithium manganese iron phosphate material, which has a simple process flow and is suitable for application in large-scale industrial production. The present disclosure further provides a lithium ion battery in which the carbon-encapsulated lithium manganese iron phosphate material is applied.