Abstract: Borax is an extremely useful industrial mineral. By analyzing the differential thermal analysis graph and dehydration graph of borax, the application of borax in diamond cutting and jewelry making field is studied. As the consequences show, borax can protect diamond from oxidizing in the process of cutting; in the process of jewelry welding it can make precious metal weld better; and in the process of precious metal smelting it can make low-priced metals separate from precious metals to become into molten slag.