The invention discloses a method for synthesizing a high tap density spinel material LiNi0.5Mn1.5O4. The method is characterized by comprising the steps of: (1) dissolving a lithium salt, a nickel salt, a manganese salt and an additive in certain proportion in deionized water, stirring and heating the water so as to form a sol mixture; (2) presintering the sol at a specific temperature for a specific period of time, thus obtaining a primary product; (3) subjecting the primary product to high temperature formal sintering for a specific period of time under a specific temperature, thus obtaining an end product. The process of the invention has the characteristics of simple gel forming method, short production period, lower energy consumption, less hidden dangers in large scale production, and low production cost, etc. And the spinel-type nickel lithium manganate positive material prepared by the method of the invention has the advantages of high product purity, high tap density, uniformproduct particle and stable electrochemical performance.