The paper described the reaction mechanism of selfbonding in dry process binderless fiberboard manufacture by infrared spectroscopy.The results showed that:1.During defibering,cellulose,hemicellulose and lignin were partly degraded.2.These degraded substances could be copolymerized during hot pressing.3.The increased hydroxyl after defibrinating partly formed hydrogen bonding during hot pressing, resulting in strengthened fiber self bonding.4.After hot pressing,there was an increase in hydrophobic carbonyl and a decrease in hydrophilic hydroxyl, which could help to explain the good waterproof ability of the board.