The invention relates to a method for preparing high-purity oxygen and aims at provides a method which has the advantages of high yield, low investment, and lower cost. According to the technical scheme of the invention, the method for utilizing the oxygen-nitrogen liquefaction device to prepare high-purity oxygen comprises the following steps: a, a first rectifying tower evaporator, a first rectifying tower, a main condensate evaporator, a second rectifying tower, and a second rectifying tower condenser are sequentially and fixedly arranged from bottom to top, and then simultaneously carry out subsequent process; b, the nitrogen output by the oxygen-nitrogen liquefaction device absorbs cold energy so as to be converted into liquid nitrogen, the generated liquid nitrogen and the liquid nitrogen output by the oxygen-nitrogen liquefaction device are combined and release cold energy, and the cold energy is converted into a gaseous form so as to be returned the oxygen-nitrogen liquefaction device; and c, the liquid nitrogen output by the oxygen-nitrogen liquefaction device release cold energy, part of components are discharged, the other gas is divided into two paths: first-path gas absorbs cold energy, part of components of the first-path enter into the atmosphere for discharge, and the other components of the first-path is further rectified; and second-path gas absorbs cold energy part of components of the second-path gas enter into the atmosphere for discharge, and the other components of the second-path gas release cold energy, thus the products are obtained.