A supercritical carbon dioxide drying technique was developed to prepare nanometer particle. The process of the technique mainly consisted of a preparation of gel in aqueous solution, filtering, replacement of the water in the precipitate with a mixture of n-propanol and benzene, supercritical drying. The technique can be industrialized easily and can be widespreadly used in the preparation of nanometer metal hydroxide, salt that are insoluble in water and propanol. Copper berate with a particle size of 10-20 nm, a surface area of 247.7 m(2)/g and a pore volume of 1.059 ml/g, was prepared using the method. The surface area and the pore volume were much larger than that of the sample prepared using precipitation method.