A method for preparing a cathode active material for lithium secondary batteries, having a core-shell multilayer structure, the method comprising the steps of: a) introducing an aqueous ammonia solution or ammonium sulfate ((NH 4) 2 SO 4), an aqueous manganese composite metal salt solution and a basic aqueous solution into a reactor having an air atmosphere, and mixing the solutions with each other in the reactor, to obtain a spherical composite metal oxide precipitate; b) mixing an aqueous ammonia solution or ammonium sulfate ((NH 4) 2 SO 4), said spherical composite metal oxide precipitate, a transition metal-containing metal salt aqueous solution and a basic aqueous solution with each other in a reactor having a nitrogen atmosphere to obtain a double layer composite metal hydroxide precipitate having a core-shell structure containing transition metal hydroxide as the shell; c) filtering said composite metal oxide-composite metal hydroxide precipitate, washing the filtrated material with water, drying the washed material to obtain a [(M x Mn 1-x) 3 O 4] 1-z [(M' y Mn 1-y) 2] z precursor, and drying or pre-heat treating the precursor, wherein M is at least one metal salt selected from the group consisting of Mg, Ca, Sr, Al, Ga, Fe, Co, Ni, V, Ti, Cr, Cu, Zn, Zr, In, Sb, P, Ge, Sn, Mo and W, M' is at least one metal salt selected from the group consisting of Fe, Co, Ni, Cu, Cr, V, Ti and Zn, 0.02≤ x ≤0.25, 0.01≤ y ≤ 0.6; and d) mixing said precursor with any one selected from among lithium hydroxide (LiOH)/lithium fluoride (LiF), lithium hydroxide (LiOH)/lithium sulfide (Li 2 S), and lithium hydroxide (LiOH)/solid sulfur, at a desired composition ratio, maintaining the mixture at 400-650 °C for 5-10 hours, grinding the resulting mixture, calcining the powder at 700-1100 °C for 6-25 hours, and annealing the calcined powder at 500-700 °C for 10 hours, wherein, reaction time in the step b) is controlled to 0.5-10 hours so that the shell portion has a thickness of the shell layer corresponding to 1-50% of the total radius of the cathode active material. a) introducing an aqueous ammonia solution or ammonium sulfate ((NH 4) 2 SO 4), an aqueous manganese composite metal salt solution and a basic aqueous solution into a reactor having an air atmosphere, and mixing the solutions with each other in the reactor, to obtain a spherical composite metal oxide precipitate; b) mixing an aqueous ammonia solution or ammonium sulfate ((NH 4) 2 SO 4), said spherical composite metal oxide precipitate, a transition metal-containing metal salt aqueous solution and a basic aqueous solution with each other in a reactor having a nitrogen atmosphere to obtain a double layer composite metal hydroxide precipitate having a core-shell structure containing transition metal hydroxide as the shell; c) filtering said composite metal oxide-composite metal hydroxide precipitate, washing the filtrated material with water, drying the washed material to obtain a [(M x Mn 1-x) 3 O 4] 1-z [(M' y Mn 1-y) 2] z precursor, and drying or pre-heat treating the precursor, wherein M is at least one metal salt selected from the group consisting of Mg, Ca, Sr, Al, Ga, Fe, Co, Ni, V, Ti, Cr, Cu, Zn, Zr, In, Sb, P, Ge, Sn, Mo and W, M' is at least one metal salt selected from the group consisting of Fe, Co, Ni, Cu, Cr, V, Ti and Zn, 0.02≤ x ≤0.25, 0.01≤ y ≤ 0.6; and d) mixing said precursor with any one selected from among lithium hydroxide (LiOH)/lithium fluoride (LiF), lithium hydroxide (LiOH)/lithium sulfide (Li 2 S), and lithium hydroxide (LiOH)/solid sulfur, at a desired composition ratio, maintaining the mixture at 400-650 °C for 5-10 hours, grinding the resulting mixture, calcining the powder at 700-1100 °C for 6-25 hours, and annealing the calcined powder at 500-700 °C for 10 hours, wherein, reaction time in the step b) is controlled to 0.5-10 hours so that the shell portion has a thickness of the shell layer corresponding to 1-50% of the total radius of the cathode active material.