NOVELTY - A biomass oil modification and 4C hydrocarbon catalytic pyrolysis combining method involves reacting oil in a hydrocarbon catalytic pyrolysis reactor with catalyst. The catalyst to be produced with low coke content is separated from reaction oil gas. Main reaction oil gas is fed into a fractionation system. Biomass oil is fed into a biomass oil pyrolysis modification reactor and reacted with the catalyst. The catalyst to be produced with high coke content is separated and mixed with the catalyst to be produced with low coke content and burnt to form a reproduced catalyst fed to the reactors.    USE - Method for combining biomass oil modification and 4C hydrocarbon catalytic pyrolysis.    ADVANTAGE - The method enables effective conversion of low-quality biomass oil into high-quality biomass oil, and utilization of excessive heat of a biomass oil catalytic pyrolysis modification device for 4C hydrocarbon catalytic pyrolysis reaction process, thus increasing the output of propylene.    DETAILED DESCRIPTION - A biomass oil modification and 4C hydrocarbon catalytic pyrolysis combining method involves feeding 4C material oil into a 4C hydrocarbon catalytic pyrolysis reactor to contact and react with a catalyst from a reproducer. The catalyst to be produced with low coke content is separated from reaction oil gas in a reactant stream and fed into the reproducer. Main reaction oil gas of the hydrocarbon catalytic pyrolysis reactor is separated and fed into a fractionation system. Low-quality biomass oil is fed into a biomass oil catalytic pyrolysis modification reactor and made to react with the catalyst from the reproducer. The catalyst to be produced with high coke content is separated from modified reaction oil so as to separate secondary reaction oil gas that is mixed with the main reaction oil gas. The main reaction oil gas is led into the fractionation system. The separated catalyst to be produced with high coke content is mixed with the catalyst to be produced with low coke content from the 4C hydrocarbon catalytic pyrolysis reactor, and the mixture is burnt in the reproducer to form a reproduced catalyst. The reproduced catalyst is fed into the 4C hydrocarbon catalytic pyrolysis reactor and the biomass oil catalytic pyrolysis modification reactor. An INDEPENDENT CLAIM is also included for a device for combining biomass oil modification and 4C hydrocarbon catalytic pyrolysis.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a device for combining biomass oil modification and C4 hydrocarbon catalytic pyrolysis.