Disclosed is a method of manufacturing iron-based powder using a molten steel. The method of manufacturing the iron-based powder according to the present invention includes providing an iron-based molten steel manufactured through a iron making process and a steelmaking process to a tundish; and performing water atomization over the molten steel discharged through a nozzle connected to the tundish. The iron-based powder is manufactured from the molten steel refined after a molten iron tapped from a iron making process is charged into a converter without a pre-treatment process of the molten iron by applying the present invention, thus economically providing the highly clean iron-based powder.