The invention discloses a lithium nickel cobalt manganese oxide precursor and a preparation method thereof. The preparation method specifically comprises the following steps of preparing a water solution of a mixed salt of nickel, cobalt and manganese as a solution A for later use, aqueous ammonia with the mass fraction of 16% as a complexing agent solution B and a sodium hydroxide solution as a precipitation solution C; firstly pumping the solution A and the solution B into a transition container at the same time and constantly stirring to obtain a mixed solution D, meanwhile, pumping the mixed solution D and the precipitation solution C into a CSTR reactor to which a base solution is added in advance at the same time, dividing the preparation process of the precursor into an early stageand a late stage, controlling reaction temperatures at different stages, continuously dropwise adding for 20-48h and constantly stirring; and finally carrying out ageing, washing, filtering and dryingon the obtained sediments to prepare the lithium nickel cobalt manganese oxide precursor with relatively good sphericity.