A method for preparing nickel-cobalt-manganese hydroxide. The method comprises the following steps: (1) dissolving microcrystalline cellulose into water to obtain a suspension; and adding a nickel source, a cobalt source, and a manganese source into the suspension to obtain a solution containing nickel, cobalt, and manganese; (2) adding hexamethylenetetramine into the solution containing nickel, cobalt, and manganese, heating the reaction solution to 80-90° C., and reacting for 5-10 min, then heating with a microwave hydrothermal synthesis instrument at a frequency of 2450 MHz for 10-60 min; and (3) filtering the reaction solution obtained in step (2), and taking the filter residue, washing the filter residue with pure water and ethanol respectively, then drying, crushing, and screening the filter residue to obtain nickel-cobalt-manganese hydroxide. Nickel-cobalt-manganese hydroxide prepared from the abovementioned method has a uniform particle size and consistent morphology and structure; thus solving the problems of the uncontrollable appearance and structure and the inconsistent performances of the product caused by the vigorous reaction in the existing method for preparing nickel-cobalt-manganese hydroxide.