The invention discloses a preparation method of a high-molecular nylon powder material used for 3D printing. The method comprises the following steps: 1)placing a nylon material, a nucleating agent and alcohol in a high pressure reaction vessel; 2)operating the high pressure reaction vessel for stirring, introducing nitrogen for protection, heating the material in the high pressure reaction vessel to 130-160 DEG C; 3)insulating and dissolving, insulating the reaction vessel for 2-3 hours, fully stirring, dissolving the nylon material; 4)cooling, depositing and precipitating, controlling the stirring speed of the high pressure reaction vessel, slowly cooling, and gradually completing the precipitation and moulding of the nylon powder; 5)filtering, cooling the material in the high pressure reaction vessel to less than 70 DEG C, transferring the mixture to a filter tank, separating the solvent from the solid; 6)centrifuging, transferring the filter residue to a centrifuge for removing the solvent; 7)drying under vacuum; thoroughly removing the solvent in a vacuum drying machine; and 8)sieving the dried nylon powder, and controlling the particle size of nylon powder at 35-50 mum to obtain the required material.