Catalytic cracking process for poor oil

A low-quality oil catalytic cracking process is characterized in that light diesel produced from the low-quality oil by catalytic cracking is partially or entirely reprocessed to correspondingly reduce the feed amount of fresh materials. As a result, the yield of light diesel is reduced greatly or even reduced to zero relevant to fresh catalytic material; the yields of liquefied gas and gasoline are improved greatly and the propylene yield is improved correspondingly; and the slurry oil can be partially reprocessed so that the light oil yield is improved greatly in comparison with the process for withdrawing all of the slurry oil. Since the yield of catalytic cracked diesel with low cetane number is reduced greatly, qualified commodity diesel can be prepared from straight-run diesel more easily by refinery plant.