To utilize the fermentation residue of corn straw, the lignin component was extracted by using alkaline-ethanol method. Effects of ethanol concentration, temperature, residue/solvent ratio and alkaline amount on lignin yield were studied. The obtained lignin was characterized by fourier transform infrared spectroscopy (FTIR), carbon-13 nuclear magnetic resonance (13C NMR) and proton nuclear magnetic resonance (1H NMR) spectroscopy. Results showed that the extraction yield of lignin could reach 93.5% and the content of lignin was up to 94.1% under the condition (temperature was 200℃, ethanol concentration was 50%, m(residue)∶m(solvent)=1:20 and NaOH concentration was 0.5wt.%). In addition, hydroxyl content of the obtained lignin product was 66.5 mg KOH/g. For the preparation of lignin-based polyurethane film, the tensile strength and the elongation at break were 24.0MPa and 224% respectively, and the degradation ratio was 3.3% when the ratio of substitution of polycaprolactone by lignin was 27%. Furthermore, the appropriate addition of glucose into the lignin-based polyurethane film can increase the biodegradation rate and water resistance of the film, reduce membrane permeability and the degradation ratio of the film with 3% glucose adding was 11.0% in 60 days.