The invention discloses a modified high-nickel positive electrode material coated with a fast ion conductor and a preparation method of the modified high-nickel positive electrode material. The high-nickel positive electrode material comprises a substrate, wherein the substrate is a compound LiNi<1-x-y>Co<x>Mn<y>M<z>O<2> shown in a formula I, in the formula I, x is more than 0 but less than or equal to 0.20, y is more than 0 but less than or equal to 0.20, z is more than 0 but less than or equal to 0.1, and M is arbitrary one or more of elements of Al, Mg, Ti, Zr, Mn, Ni, Sn, Co, Zn, W, Mo, Ru, Ca, Sr, Ba, B, Y, V and Nb. The preparation method comprises the following steps of washing and drying the high-nickel positive electrode material, uniformly mixing the high-nickel positive electrode material and an appropriate amount of coating agent, and performing sintering and sieving to obtain the modified high-nickel positive electrode material coated with the fast ion conductor. The fastion conductor is coated by washing and surface drying methods, the alkali amount of a surface of the positive electrode material is reduced, side reaction of the material and an electrolyte is reduced, and the high-temperature stability and the safety of the material are improved; and by doping and coating the surface with the fast ion conductor, the energy density, the rate performance and the cycle property of the material are improved, and the long cycle lifetime of a battery is finally prolonged.