Abstract: Ru/HZSM-5 was prepared and used to upgrade bio-oil online and the changes of bio-oil yield and physicochemical properties were analyzed through the total quality index ( TQI ). The changes of the chemical compositions of the bio-oils were compared; simultaneously, the coking situation of the catalyst was characterized. The results showed that the yield and physicochemical properties of bio-oil obtained by using fresh catalyst were high, and the TQI increased from 0.15 to 6.45; with the increase of using times, the TQI first increased slightly to 6.68, then decreased rapidly to 1.25, and reduced to only 0.27 after the fourth usage. In the initial stage, a small amount of coking reactions made the strong acid sites partially passivated, which improved the aromatization performance. When the catalyst was used twice, the relative content of hydrocarbons in the bio-oil reached 53.79%, of which the relative content of light aliphatic hydrocarbons was 16.87%, and the relative content of monocyclic aromatic hydrocarbons was 32.65%. After the fourth usage, the relative content of hydrocarbons in the bio-oil was only 9.32%, and the catalyst layer basically lost the upgrading effect, and had adverse effects on pyrolysis vapors such as secondary cracking or polymerization. Before the third usage, the low-temperature pyrolytic coke attached to the catalyst surface was dominant. After the third usage, the low-temperature pyrolytic coke and high-temperature catalytic coke increased significantly, and the catalyst activity decreased sharply. Continuous usage of catalyst slightly increased coke, of which the pyrolytic coke increased mainly.