Disclosed is a method of storing a thioepoxy compound and a method of preparing a thioepoxy based optical material using the thioepoxy compound. Particularly, a method of preparing a high-quality thioepoxy based optical material having superior color and thermal stability and less time-dependent change, and being colorless and transparent by inhibiting time-dependent change of the thioepoxy compound during storage is disclosed. In addition, a method of storing the thioepoxy compound for an optical material, the thioepoxy compound having a water content of 500 to 2,500 ppm and stored at −78 to 10° C., and a method of preparing the thioepoxy based optical material, the method including polymerizing a polymerizable composition including the stored thioepoxy compound, are provided. The high-quality thioepoxy based optical material, which is colorless and transparent, prepared according to the present invention may be broadly used in a variety of fields as a substitute for conventional optical materials.