The invention relates to a method for preparing a phase transition storage, which comprises the steps of: applying the CVD technique to deposit SiO2/S3N4/SiO2 medium layers on a substrate in sequence,then using submicron CMOS standard process exposure technique to prepare pores with a diameter ranging from 150 to 300nm on the top SiO2 layer, and then depositing S3N4 with a thickness ranging from100 to 200nm and etching the S3N4 along with the S3N4 deposited at the very beginning to form S3N4 side walls with a thickness ranging from 50 to 150nm in the holes, finally, finishing etching the bottom SiO2 layer by taking the S3N4 side walls as a hard mask, filling electrode materials such as W, TiN and the like by using the CVD technique and conducting chemical-mechanical polishing and stopping on the bottom SiO2 layer to form prismatical heating electrodes with a diameter less than 100nm. The method for preparing the phase transition storage not only avoids the difficulty of directly using the exposure technique less than 100nm and reduces the manufacturing cost, but also more importantly reduces the operating current and the power dissipation of the phase transition storage.