Abstract: Three inferior heavy oils from Venezuela, Liaohe and Karamay were chosen as the feedstocks, and the effect of heavy metals on the characteristics of coke formation during thermal conversion process was studied. The results indicate that the higher content of heavy metals, the shorter coke induction period. With the increasing of the content of heavy metals, the yield of coke is increased obviously; the coke particle size becomes larger. Furthermore, the analysis of product from the delayed coking process indicates that the oil with higher content of heavy metals produces a higher coke yield, but a lower yield of liquid.