A method for preparing a nano super-conducting composite for a magnetizer comprises the following steps: S1, preparation of a nano composite powder material: making dysprosium, cobalt, metallic hydrogen, black phosphorus and nickel alkene into nano powdery materials, and uniforming mixing the prepared powdery materials of dysprosium, cobalt, metallic hydrogen, black phosphorus and nickel alkene according to the preset proportion (molar ratio) of 0.1-5 of dysprosium, 0.5-20 of cobalt, 1-15 of metallic hydrogen, 20-80 of black phosphorus and 1-20 of nickel alkene; S2, metallurgical high-pressure die-casting of nano powder: making the powdery composite uniformly mixed in the S1 into a powder billet, and performing high-pressure die-casting on the powder billet at 1-100 GPa; and S3, high-temperature high-pressure vacuum plasma sintering sizing: performing high-temperature plasma sintering sizing on the die-cast powder billet at 1,500-3,000 DEG C in a vacuum environment with the pressure intensity of 1-100 GPa to obtain the nano super-conducting composite with the required physical and mechanical properties.