A method for preparing a spherical cathode active material for secondary lithium batteries comprising a multilayer core-shell structure having a structural formula of: Li 1+a [(M x Mn 1-x) 1-z (M' y Mn 1-y) z] 2 O 4 (M is a metal selected from a group consisting of Ni, Co, Mg, Zn, Ca, Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr, Ge, Sn and combinations thereof, M' is a metal selected from a group consisting of Ni, Mg, Cu, Zn and combinations thereof, M' is different from M, 0.01≤x≤0.25, 0.01≤y≤0.5, 0.01≤z≤0.5, and 0≤a≤0.1), which is characterized in that the method comprises: a) mixing and stirring distilled water and a hydrazine (H 2 NNH 2) solution in a reactor, feeding a metal salt solution containing a Mn salt and a salt of a metal M selected from a group consisting of Ni, Co, Mg, Zn, Ca, Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr, Ge, Sn and combinations thereof, and an aqueous ammonia solution into the reactor, and adding a mixture of a carbonate solution and a hydrazine solution to the reactor, so as to cause a reaction; b) ceasing the supply of the metal M and Mn, and feeding a metal salt solution containing a Mn salt and a salt of a metal M' selected from a group consisting of Ni, Mg, Cu, Zn and combinations thereof, a carbonate solution and an aqueous ammonia solution into the reactor to cause a reaction for producing a complex transition metal carbonate particle having a composition of [(M x Mn 1-x) 1-z (M' y Mn 1-y) z]CO 3; c) filtering, washing and drying the complex transition metal carbonate particle to obtain a precursor having a composition of [(M x Mn 1-x) 1-z (M' y Mn 1-y) z] 2 O 3; and d) mixing the precursor with a lithium salt selected from a group consisting of lithium hydroxide (LiOH), lithium carbonate (Li 2 CO 3), and lithium nitrate (LiNO 3), and heating to a temperature ranging from 400 to 650°C, maintaining the temperature thereat for a predetermined period of time, grinding and calcining the mixture. a) mixing and stirring distilled water and a hydrazine (H 2 NNH 2) solution in a reactor, feeding a metal salt solution containing a Mn salt and a salt of a metal M selected from a group consisting of Ni, Co, Mg, Zn, Ca, Sr, Cu, Zr, P, Fe, Al, Ga, In, Cr, Ge, Sn and combinations thereof, and an aqueous ammonia solution into the reactor, and adding a mixture of a carbonate solution and a hydrazine solution to the reactor, so as to cause a reaction; b) ceasing the supply of the metal M and Mn, and feeding a metal salt solution containing a Mn salt and a salt of a metal M' selected from a group consisting of Ni, Mg, Cu, Zn and combinations thereof, a carbonate solution and an aqueous ammonia solution into the reactor to cause a reaction for producing a complex transition metal carbonate particle having a composition of [(M x Mn 1-x) 1-z (M' y Mn 1-y) z]CO 3; c) filtering, washing and drying the complex transition metal carbonate particle to obtain a precursor having a composition of [(M x Mn 1-x) 1-z (M' y Mn 1-y) z] 2 O 3; and d) mixing the precursor with a lithium salt selected from a group consisting of lithium hydroxide (LiOH), lithium carbonate (Li 2 CO 3), and lithium nitrate (LiNO 3), and heating to a temperature ranging from 400 to 650°C, maintaining the temperature thereat for a predetermined period of time, grinding and calcining the mixture.