The methods of synthesizing polyurethane (Isophorone diisocyanate IPDI) with paper were investigated. The combination of SEM and IR analysis were used to analyze the chemical and physical characteristics and forming mechanism of the polyurethane derived from paper. The physical of base-paper material improved remarkably on the conditions of dosage of IPD 12%, reaction time 10min and temperature 60°C, facture length elevated by54.4%, folding strength raised by 12.4 times, and wet strength / dry strength was 50.54%.It was found that carbonate bond was formed between IPDI with cellulose in fibers when the paper was treated with IPDI .The treatment can change hydrogen bonds into chemical bonds and enhance the base-paper material’s physical strength. The Hydroxyl of Cellulose and －N=C=O produced the structure of amino formic acid ester, which formed as a bridge between the fibers. The hydrogen combining was transformed to chemical combining, which strengthened the intensity of single fiber and reinforce the combine of fibers. The treatment can change hydrogen bond into chemical bond and improved the paper’s physical strength, especially the wet strength.