Abstract: Residue oil was cracked in H2 atmosphere at high temperature for examining its thermal cracking performance in a pilot plant in a once-through way. A residue oil with high metal content (Ni+V=232.86 μg/g) and high carbon residue (19.67%) was used as feedstock. The investigation focuses on the changes of feed conversion and removal of carbon residue, sulfur and metal. The test results indicate that the conversion and desulfurization of feedstock increase and carbon residue and metals in produced oil decrease with the increase of temperature. However, the conversion and desulfurization of feedstock decrease as the liquid hour space velocity increases. High temperature and low velocity can improve the conversion and impurities removal. There are obvious changes in conversion and impurities removal of feedstock in the range of 400～420 ℃ and 1.0～1.5 h-1. The conversion of feedstock can reach to 60%, desulfurization up to 33% and the contents of carbon residue, nickel, vanadium in the cracked oil are 11%, 28 μg/g, 72 μg/g, respectively at conditions of 420 ℃ and 1.0 h-1.