The invention belongs to the field of anode materials of lithium ion batteries, and provides a method for preparing large-granularity cobaltosic oxide. The method adopts a cobalt solution with certainconcentration as a cobalt source, a sodium hydroxide solution as a precipitator, an ammonia solution as a complexing agent and a hydrazine hydrate solution as a reducing agent, and comprises the following steps: adding a certain amount of cobalt hydroxide flashing dry dust collecting material and the hydrazine hydrate solution into a reaction kettle when synthesis is started; transforming the dust collecting material into a cobalt hydroxide precursor seed crystal under intense stirring, and synthesizing a cobaltosic oxide precursor product with the granularity of 16-18mu m by a wet method through a certain process condition; adding a certain amount of conductive carbon black into the reaction kettle after synthesis is completed, aging for a period, washing and drying the mixture, and calcining under a certain condition to obtain the large-granularity cobaltosic oxide product. By utilizing the process, the spherical or sphere-like cobaltosic oxide product having a laser granularity of16-18mu m, tap density of more than 2.0g/cm<3> and specific surface area of 1.0-3.0m<2>/g can be prepared.