Abstract: Abstract: The interaction among three biomass components (hemicellulose, cellulose, and lignin) in autoclave was studied in detail on the basis of the extreme vertices of a constrained region. Such interaction was found to have a distinct effect on product yield and characteristics. The yield of heavy oil was highest when the mixing proportion of the three components was 0.2:0.4:0.4 at 40.10 wt.%, and was lowest when the mixing proportion was 0.65:0.25:0.1 at 28.20 wt.%. When the mixing proportions were 0.3:0.2:0.5 and 0.2:0.3:0.5, the yield of the solid residue was as high as 14.00 wt.%. In the mixing experiment of the three components, when the cellulose proportion was high, the heavy oil and solid residue yields were low, whereas those of light oil and gas were high, which indicated that cellulose was first hydrolyzed into sugar products through hydrothermal conversion. The comparison results of the mixing and single-component experiments showed that when cellulose, hemicellulose, and lignin were mixed in different proportions to form biomass, the yield of heavy oil increased, whereas that of solid residue decreased. The yields of light oil and gas were between those of cellulose and lignin. Results of gaseous products show that products from cellulose hydrolysis could promote hemicellulose hydrolysis and generate large amounts of CO2. The interaction between cellulose and hemicellulose under different mixing proportions increased the CO2 yield compared with that of the single component. Relatively, the influence on CO, CH4, and CnHm was weak. The lignin content, as well as the low cellulose and hemicellulose contents, inhibited the acid and ketones in light oil. High lignin content could promote the hydrolysis of cellulose and hemicellulose to produce acids, and the interaction among the three components inhibited the generation of acids. In addition, the lignin proportion also affected the relative acids. When the lignin proportion was greater than 0.4, the inhibition effect of the interaction on the acids weakened. In addition, the interaction among cellulose, hemicellulose, and lignin inhibited the production of acid compounds in heavy oil and promoted phenolics. The acid in the heavy oil of lignin was mainly homovanillic acid about 9.07%. When lignin, hemicellulose, and cellulose were mixed with certain proportions, the acid in the heavy oil reduced. After mixing, the homovanillic acid was highest at only 2.4%, which indicated that the interaction among the three components inhibited the generation of acids in heavy oil, thus, improving the heavy oil quality. The interaction among the three components promoted a series of hydrolysis product reactions, such as polymerization and condensation, to generate char, thus resulting in a high degree of aromatization. The hemicellulose in the mixed proportion slightly influenced the infrared absorption peak of the char. The absorption peaks under the 1-11 mixing proportions were stronger than that of the single hemicellulose. Hemicellulose was hydrolyzed completely at 200 to 230℃ to generate gas and liquid products with CO2 and small molecular oxygen compounds as the primary outcomes, namely, sugars, acids, aldehydes, and phenols. These compounds had certain promoting functions in the hydrolysis of cellulose and lignin, and caused new condensation and polymerization on hydrolysis products to generate a solid residue.