The invention relates to a lithium-rich manganese-based cathode material with a crosslinking structure and a preparation method thereof. The preparation method specifically comprises the following steps of (1) preparing a mixed reaction solvent of deionized water and organic alcohol; (2) mixing and dissolving soluble nickel, cobalt and manganese salts into the mixed reaction solvent; (3) heating the mixed reaction solvent to the reflux state by a microwave radiation manner; (4) under the continuous reflux state, adding an alkaline resource, and maintaining reaction, so as to obtain a nickel, cobalt and manganese hydroxide precursor; (5) fully mixing the nickel, cobalt and manganese hydroxide precursor and a lithium source, and calcining, so as to obtain the final lithium-rich manganese-based cathode material. The prepared lithium-rich manganese-based cathode material has the advantages that a crosslinking net-shaped structure is formed, the pore radius is rich, the crystallizing degreeis high, and the lithium ions are quickly disembedded and embedded at low resistance; the method for preparing the precursor of the lithium-rich manganese-based material is simple, the time is short,the organic solvent can be repeatedly recycled and used, the cost is reduced, the environment-friendly effect is realized, and the production efficiency is greatly improved.