Low-grade heavy oil catalytic conversion process for increasing yield of low-carbon olefins and diesel oil

The invention relates to a low-grade heavy oil catalytic conversion process for increasing the yield of low-carbon olefins and diesel oil. The process comprises the following steps: (1) preheated low-grade heavy oil, namely raw oil, enters a zone I of a riser and is in high-temperature short-contact-time high-agent-oil ratio contact with a catalytic cracking catalyst, so as to be subjected to catalytic cracking reaction, and generated oil and gas enter a fractionating tower; (2) a top outlet material of the fractionating tower is a mixture of dry gas, liquefied gas and gasoline, a middle-part outlet material of the fractionating tower is diesel oil, a lower-part outlet material of the fractionating tower is catalyzing wax oil which is relatively difficult to crack, a bottom outlet material of the fractionating tower is oil slurry, the catalyzing wax oil enters a zone II of the riser, and the oil slurry enters a vacuum distillation tower; (3) an upper-part outlet material of the vacuum distillation tower enter