The invention discloses a garnet-type ion conductor-coated high-nickel ternary positive electrode material, a preparation method and a lithium ion battery obtained by preparation. A matrix of the garnet-type ion conductor-coated high-nickel ternary positive electrode material is LiNi<1-x-y>Co<x>Mn<y>O<2-z>Ha<z>, wherein x is more than 0 but less than or equal to 0.15, y is more than 0 but less than or equal to .15, z is more than 0 or less than or equal to 0.04, Ha is one or more of F, Cl, Br, the chemical formula of a garnet-type ion conductor is one or more of Li<7-a>La<3>Zr<2-a>MaO<12>, Li5La3M2O12, Li<5.5>La<3>M<1.75>A<0.25>O<12>, Li6DLa2M2O12, Li<7.06>M<3>Y<0.06>Zr<1.94>O<12> and Li<7.06>La<3>Y<0.06>Zr<1.94>O<12>, M is Nb or Ta, A is In or Zr, D is Ca, Sr or Ba, and a is more than orequal to 0 but less than or equal to 1. By direct mixing and coating of a garnet-type coating agent and the ternary material, a sintering temperature is lower than 700 DEG C, the damage to a crystal structure of the ternary lithium nickel-cobalt manganate material is prevented, and the rate performance and the cycle performance of a lithium ion battery are improved.