The degradative solvent extraction (DSE) has been found to be an effective method to convert and upgrade biomass wastes into high-quality extracts with various applications. However, the reaction pathways and kinetics of this DSE process are still not clear and need to be clarified. Hence, in this study, the biomass was treated in 1-methylnaphthalene at various conditions (300-350 degrees C and 0-90 min) by the DSE method and separated into five products: residue (unreacted biomass), two extracts (deposit and soluble), liquid, and gas. A lumped reaction model was proposed to simulate this biomass DSE process. The kinetic parameters were estimated by the least squares fit based on the experimental data and the model, which was optimized by the MATLAB optimization program. The results showed that the proposed model was valid and well-capable of describing the biomass DSE process. It can be concluded that different conversion pathways existed at 300 and 350 degrees C. At 300 degrees C, the dominant reactions were the conversion of residue (unreacted biomass) to the extraction products [deposit (k = 0.0104 min(-1)), soluble (k = 0.0042 min(-1)), and liquid (k = 0.0044 min(-1))]. The deoxygenation reactions mainly occurred at relatively mild conditions. While at 350 degrees C, the rate-controlled process was the conversion of high-molecular-weight extract (deposit) to low-molecular-weight extract (soluble) (k = 0.0155 min(-1)). A comprehensive understanding of the reaction pathways of the biomass DSE conversion process was provided.