The invention discloses a Mo-assisted co-doped disordered rock salt Li1. 3Mn0. 4Nb0. 3O2 lithium-rich positive electrode material as well as a preparation method and application thereof. The preparation method comprises the following steps: taking metal oxides such as Li2CO3, Mn2O3, Nb2O5, MoO2, SnO2 and Fe2O3 as precursors, weighing according to a specific stoichiometric ratio, and additionally adding about 10% of Li2CO3 to compensate for Li loss; the preparation method comprises the following steps: fully mixing, carrying out high-energy ball milling in an argonatmosphere, tabletting, heating to 1000 DEG C at a speed of 5 DEG C / min in the argonatmosphere in a tubular furnace, calcining for a certain time at a constant temperature, naturally cooling, and rapidly transferring to a glove box. The positive electrode material is used for the lithiumion battery, the charge-discharge specific capacity and the energy density of the lithiumion battery can be improved, the preparation process is simple, the cost is low, and large-scale production is easy.