Al8B4C7 should be a successful antioxidant in carbon-containing refractories, and it have excellent hydration resistance. In this paper, the synthesis process of Al8B4C7 and the mechanism have been studied. Aluminum, borax and activated carbon powders were used as starting material. Using borax as the source of B, can greatly reduce the cost of synthesis. Our experiments showed that use these materials can synthesize Al8B4C7, and the final product is closely related to the temperature and ratio of raw materials. Al8B4C7 appeared at about 1300°C, and with the temperature increased, more Al8B4C7 was generated in the heating samples. The phase compositions of these samples heated at 1700°C were Al8B4C7, Al2O3, Al4O4C and Al2OC.