Abstract: The aim of this paper is to establish the main reaction pathway chart when the cornstalk is liquefied in the sub-and super-critical ethanol, and research the mechanism how the ethanol exert an influence on the products in the reaction. With the principle of lump, five lumps were defined based on the characteristics of the material and products, and they were gas, organic dissolved, heavy oil, volatile organic compounds and residue. According to the study of products yield of a series of liquefaction (a series of calefaction and a series of reaction) and effect of the content of ethanol on products yield, the lumped components of complex reaction system were defined and a reaction network was proposed. The results showed that the main reactant was cornstalk water soluble extracts before the reaction temperature came to 180℃ and the main products were gas, volatile organic compounds and a little heavy oil. Then the three main components of cornstalk (cellulose, hemicellulose, lignin) began to react after the reaction had came to 180℃, and the main products were gas, volatile organic compounds, heavy oil and organic dissolved. In the liquefaction process there was reversible reaction between the heavy oil and volatile organic compounds; organic dissolved was mainly transformed into gas in the secondary reaction. In the liquefaction process ethanol not only transferred heat, acted as the solvent of the reaction, but also supplied radicals for the reaction, and these radicals restructured the products of the liquefaction.