Disclosed is a method for preparing a precursor of lithium composite transition metal oxide for lithium secondary batteries, using a reactor having a closed structure including an outer stationary cylinder; an inner rotary cylinder on the same axis; and a rotation reaction area disposed between them, wherein ring-shaped vortex pairs that are uniformly arranged in a rotation axis direction and rotate in opposite directions are formed in the rotation reaction area. According to the method of the invention, raw materials comprising an aqueous solution of two or more transition metal salts, an aqueous solution of a complex forming additive, and a basic aqueous solution for maintaining pH are fed through an inlet into the rotation reaction area where a coprecipitation reaction is performed under a non-nitrogen atmosphere to form lithium composite transition metal oxide particles which are then discharged through a reactor outlet.