Abstract: In this paper, the property of coke from ethylene cracking and changes of its microcosmic structure in the combustion process with and without combustion-supporting agent were studied. The coke combustion rate at the end is much smaller than that at the beginning. Coke from ethylene cracking can't be exhausted by combustion, leaving 5% combustin residue. After the addition of combustion-supporting agent, the original microcosmic structure of coke is broken, thus not only increases the combustion rate, but also increases the burn-off rate of the coke.