A method of reforming a heavy hydrocarbon distillate, which includes treating a heavy hydrocarbon distillate and a lignocellulosic biomass with a solvent, is provided.The method can be useful in maximizing conversion of the heavy hydrocarbon distillate into higher value-added distillate, for example, naphtha and a middle distillate, and allowing a sulfur compound produced by the decomposition of a heavy hydrocarbon distillate to catalyze pretreatment of the lignocellulosic biomass.Also, oxygen, hydroxymethylfurfural (HMF), levulinic acid, formic acid, and sulfuric acid produced by decomposition of the lignocellulosic biomass can catalyze decomposition of a heavy hydrocarbon distillate and lignocellulosic biomass, thereby activating decomposition of a heavy hydrocarbon distillate.