A method for preparing Li.sub.1+xNi.sub.1-yCo.sub.yO.sub.2 cathode materials is disclosed, wherein -0.2.ltoreq.x.ltoreq.0.2 and 0.05.ltoreq.y.ltoreq.0.5. The method includes the following steps: (A) adding a first solution into a second solution to form a mixed solution, wherein the first solution is a saturated lithium hydroxide solution, the second solution contains nickel salt and cobalt salt, the mole ratio of the lithium ion in the first solution to nickel ion and cobalt ion in the second solution ranges from 1.5:1 to 5:1, and the molar ratio of nickel ion to cobalt ion in the second solution is 1-y:y; (B) stirring the mixed solution; (C) filtering the mixed solution and obtaining a co-precipitated precursor, wherein the molar ratio of lithium ion:nickel ion:cobalt ion is 1+x:1-y:y; and (D) heating the co-precipitated precursor at a temperature higher than 600.degree. C.