The invention discloses a method for producing lithium manganate as a lithium battery cathode material through wet mixing. The method comprises the following steps: at first, preparing a LiOH solution, adding a solid-phase MnO2 as a crystal nucleus, separating out a LiOH*H2O crystal from the LiOH solution, and growing on the surface of a MnO2 particle to uniformly and sufficiently mix LiOH and MnO2; after evaporating till the solution is completely evaporated to dryness, sintering, crushing and screening twice to obtain the product. The method overcomes the phenomenon that solid-phase mixed materials are mixed non-uniformly, and improves the mixing uniformity of raw materials, thereby improving the quality of the lithium manganate product, and the gram volume of lithium manganate reaches 128 mAh/g.