The gasification of petroleum coke (petcoke) can cause fouling and erosion problems. In this study, the evolution of Ni and V during steam gasification is investigated in a fluidized bed from 800 to 1100 degrees C. The occurrence modes determined by the sequential extraction show that raw petcoke contains diversified Ni forms, whereas V is dominated by organic matter and residual form. The organic matter is rapidly converted to residual form. The Ni in residual form is partially released, whereas the V in residual form is considerably converted to other forms. The volatilization of Ni is positively correlated with the temperature and sulfur content, whereas V has a positive correlation with the exchangeable form. The exchangeable form of V is conducive to forming a well-developed pore structure, whereas carbonates play the opposite role. Under the practical fluidized bed gasification, Ni tends to cause erosion, especially for continental petcoke, whereas V is inclined to cause slagging and fouling.