The invention discloses cobalt powder with fine-grained aggregate morphology and a preparation method thereof, which belong to the technical field of the preparation of alloy powder. The morphology of the cobalt powder prepared by the method is fine-grained aggregates, and the fine-grained grains forming cobalt powder aggregates have spherical or spherical-like shapes, wherein the diameter of the single fine-grained grain is between 0.1 and 0.5 mu m, and the Fisher granularity of the aggregate cobalt powder is between 0.5 and 1.5 mu m. The preparation method comprises the steps of: performing a precipitation reaction of soluble cobalt salt aqueous solution and precipitator solution; performing solid-liquid separation on a precipitate through a centrifugal machine, and washing residual acid radical ions and other impurities in the precipitate repeatedly; and performing low-temperature drying on the precipitate after centrifugation and washing for high-temperature calcination to prepare oxide, and finally reducing the oxide to cobalt metal powder by using hydrogen. The cobalt powder provided by the invention has the shape of the fine-grained aggregates, and has the advantages of high surface activity, simple production process, low cost and easy realization of industrialization.