Abstract: The experience of processing ultra-heavy oils blending large proportion of diesel fraction in the delayed coking unit of Karamay Petrochemical Company was summarized. The problems of over-current in electrostatic desalting unit, exceptional running of equipments, entraining fine coke powder in oil vapor and lower diesel yield were caused by the blending of diesel. After controlling throughput, optimizing the heat exchanger system and revamping the side-cut of distillation unit, the CGO yield is reduced and the gasoline and diesel yield exceed the analog value. Furthermore, product distributions are optimized and the operation cycle of the unit is prolonged.