Abstract: In order to meet the market demand, the joint optimization of the diesel hydrofining unit and hydrocracking unit was carried out by mixing the middle distillate of diesel hydrofining unit into feed of hydrocracking unit. The results showed that after optimization, the yield of the diesel product decreased by 6.78 percentage points, the flash point (closed) increased from 65 ℃ to 77.5℃，the kinematic viscosity increased from 3.010 mm²/s to 3.540 mm²/s, and the yield of jet fuel increased by 5.08 percentage points, meeting the expected targets of improving diesel quality, reducing diesel and increasing jet fuel production.

Key words: hydrocracking, hydroupgrading, jet fuel, diesel, joint optimization