Abstract: The behaviors of thermal-oxidation, UV photolysis and hydrolysis of straw alkali-lignin modified polyurethane films (PUF) were tested respectively. The results show that the retain ratio of tensile strength of thermal-oxidation samples with addition of 20% lignin was enhanced from 89.3% to 132.0% comparied with pure PUF and the retain ratio of elongation was from 19.6% to 66.3%, as well as from 9.4% to 48.6% under UV for 28 d. The retain ratio of tensile strength after hydrolysis, was enhanced from 74.8% to 95.5%. However, the addtion of alkali-lignin reduced remarkably the alkali resistance of PUF.