Abstract: The fluidized bed residue hydrotreating technology has a remarkable effect on the desulfurization and quality improvement of coking feedstock. The high quality coke prepared by combined process of ebullated bed hydrocracking and delayed coking was investigated and the coking law of unconverted oil（UCO） from ebullated bed was explored. The results showed that the temperature increase or the space velocity decrease were beneficial to residue conversion and impurity removal in the ebullated bed hydrogenation process. Within the same operating range，residue conversion rate was significantly higher than the impurity removal rate. With the increase of residue conversion，sulfur content of UCO decreased first and then increased. In the process of UCO coking，about 60% of sulfur from UCO was transferred into coke，higher than the sulfur ratio into the coke from residue coking process（about 42%），and the quality of petroleum coke prepared by UCO can be significantly improved compared with residue as feed. The yield and sulfur content of petcoke from UCO feed has a good linear relationship with carbon residue and sulfur content of UCO，which can be used to guide the optimization of ebullated bed hydrocracking process according to the required low sulfur coke grade.

Key words: ebullated bed hydrocracking, delayed coking, low sulfur coke, sulfur transfer, coking coefficient