The invention discloses a lithium ion phosphate positive electrode material of a nanometer core shell structure. The positive electrode material is provided with an inner core active material and a conductive outer shell structure; a conductive agent is an outer shell material; the active material is of an inner core structure; and the structure formula of the inner core active material is LiFe[1-x]MxP[1-y]AyO4, wherein x is greater than or equal to 0, y is less than or equal to 0.1, M is a transition metal element, and A is silicon. Additionally, the invention also discloses a preparation method of the lithium ion phosphate positive electrode material. According to the preparation method in the invention, a porous material is adopted as a synthesis microreactor, and a lithium ion phosphate precursor is loaded and filled in holes, namely, the inner core active precursor reversely wraps a porous precursor so as to form a special nanometer core shell structure, thus the topography granularity of primary granule is controlled; and the lithium ion phosphate positive electrode material of the nanometer core shell structure is prepared by adopting a liquid phase mixed material and solid phase sintering technology. According to the invention, on the premise that the electrical performance of the positive electrode material is not influenced, a nanometer core shell structured active substance with uniform and controllable topography and granularity is synthesized; and the preparation method disclosed by the invention has lower technology, devices and control costs, which is beneficial to large-scale production.