Abstract: The corn stalk was used as the raw material and the deionized water was used as the medium to study the effect of aqueous phase recirculation on characteristics of bio-crude oil formation during hydrothermal liquefaction of corn stalk. No additional deionized water was added during the recirculation. The results show that the aqueous phase recirculation can enrich the concentration of organic acids in aqueous phase and promote the conversion of ketophenols, which can improve the yield and quality of bio-crude oil and solid products. Specifically, the aqueous phase recirculation has little effect on the pH value of the aqueous phase (3.62-3.91), but the organic acids such as acetic acid and propionic acid are continuously accumulated and the content of ketones and phenols is gradually reduced. Also, the yield of bio-crude oil is gradually increased from 20.42% to 24.31%, the quality of bio-crude oil is slightly improved, and the carbon content of the solid product is increased from 60.94% to 61.74%.