The invention discloses a preparation method of composite powder. The preparation method comprises the steps that flux-cored wire is used as a raw material, then the flux-cored wire is melted to formliquid drops through thermal spraying, and the liquid drops are directly sprayed in a vacuum environment or a gas atmosphere to condense to form the composite powder. According to the preparation method of the composite powder, the raw material is simple in composition, and the process is simple and convenient; the prepared composite powder is in a spherical shape and has a core-shell structure, the particle size ranges from 10 microns to 100 microns, and the particle size range can be adjusted by changing the preparation process parameters; and the composite powder is suitable for 3D printingtechnology.