Abstract: In order to study the steam injection pressing self-bonding mechanism of bindless tobacco stem particboard, bindless tobacco stem particleboard was prepared by steam injection pressing in this paper. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), high performance liquid chromatography analysis (HPLC) and specific surface area (BET) were used to analyze the self-bonding mechanism of bindless tobacco stem particboard. The results showed that: the number of active hydroxyl in cellulose molecule was increased by the synergistic effect of the water and heat, active hydroxyl groups could form hydrogen bonds (O-H…H), van der Waals forces was formed between each of the two tobacco stem particles in the process of steam injection pressing; part of hemicellulose in tobacco stem particle was hydrolyzed by the synergistic effect of the water and heat, the hydrolysate could be subjected to polycondensation reaction to generate polycondensation furan resin which was similar to adhesives, the hydrolysate also could be subjected to polycondensation reaction with the lignin having a phenolic hydroxyl structure to generate a kind of condensation compound which was similar to phenolic resin adhesive. In addition, the lignin in tobacco stem particle was fully expanded and part of lignin was evenly distributed between each of the two tobacco stem particles by the synergistic effect of the water and heat, which could improve the physical and mechanical properties of bindless partcleboard to some extent.