The invention relates to a method and a system for increasing the yields of low-carbon olefins and aromatic hydrocarbons. The method comprises: separating a diesel oil raw material into a light dieseloil distillate and a heavy diesel oil distillate; carrying out hydrofining treatment on the obtained heavy diesel oil distillate to obtain a hydrofined product; carrying out a first catalytic cracking reaction on the obtained hydrofined product; carrying out a second catalytic cracking reaction on the obtained first catalytic cracking product and a semi-spent catalyst; carrying out a third catalytic cracking reaction on the obtained light diesel oil distillate to obtain a third catalytic cracking product and a second spent catalyst; and separating the obtained second catalytic cracking product and the obtained third catalytic cracking product to obtain a low-carbon olefin product, a light naphtha product, a heavy naphtha product, a circulating oil product and an oil slurry product. The method and the system provided by the invention can improve the yields of propylene, butene and aromatic hydrocarbon.