The invention relates to a halogen anion doped lithium-rich positive electrode material of a secondary battery as well as a preparation method and an application of positive electrode material. The expression formula of the halogen anion doped lithium-rich positive electrode material is Li[Li(1-2x)/3MxMn(2-x)/3]O2-zAz, wherein M is at least one or a combination of Co, Ni, Al, Mg, Zn, Ga, B, Zr, Ti, Ca, Ce, Y and Nb, A is at least one or a combination of Cl, Br or I, x is greater than 0 and less than 0.5, and z is greater than 0 and less than or equal to 0.5; when M is one or the combination of Ni and Co and A is Cl, x is not equal to 0.2. The preparation method comprises the following preparation steps: in the process of preparing a lamellar lithium-rich oxide positive electrode material Li[Li(1-2x)/3MxMn(2-x)/3]O2, introducing halogen anions A according to the stoichiometric ratio to prepare a solution, and then carrying out solidification, drying and calcination, thereby obtaining the halogen anion doped lithium-rich positive electrode material. If the halogen anion doped lithium-rich positive electrode material is used as the positive electrode material for a lithium battery, the first charge-discharge efficiency of the material can be improved; the structural transformation of the material in electrochemical cycle is inhibited. The electrochemical properties of the lithium-rich lamellar oxide positive electrode material are improved, and the lithium-rich lamellar oxide positive electrode material has the characteristics of high first charge-discharge efficiency, high capacity, good cycle performance, simple preparation process, good reproducibility and the like.