Method for preparing light oils from heavy oil modified with alkali under hydrothermal conditions

The invention relates to a method for preparing light oils from heavy oil modified with alkali under hydrothermal conditions. The method comprises the following steps: firstly, mixing alkali and water to prepare heavy oil modifying alkali liquor; and secondly, mixing alkali liquor and heavy oil in a volume ratio of 1:0.5-1:10 to preheat, then sending to a hydrothermal reactor, treating at 280-480 DEG C under 10-35MPa for 0.2-8h, separating the three phases of the treated product, namely the gas phase, the aqueous phase and the oil phase, and performing distillation to the product oil to obtain light oils such as gasoline and diesel oil. Compared with the prior art, the heavy oil modifying method of the invention can be performed under subcritical and supercritical hydrothermal conditions; and by using alkali, the coking of heavy oil can be effectively avoided, the yield of light oils can be increased and the removal effect of the impurities in heavy oil is better.