Lignin was isolated from poplar sawdust using maleic acid pretreatment, then mechanically mixed with nannocellulose according to different contents to prepare nanocellulose/lignin composite film by filtration and drying process. The microstructure, mechanical property, optical property and thermal stability of the materials were tested by scanning electron microscope, universal tensile testing machine, ultraviolet spectrophotometer, spectrodensitometer and thermogravimetric analyzer. The results showed that the surface of pure CNF film was smooth and dense, while the addition of lignin made film rough with increasing root mean square (RMS) roughness value from 19.8 to 62.7 nm. With the increase of lignin content, the tensile strength of the composite films were decreased from 140 to 67.6 MPa. When the lignin content was 5%, the Young's modulus was up to 7.11 GPa. In the meantime, lignin endowed composite film with excellent ultraviolet shielding properties with UVA and UVB blocking rate of 99.23 and 100%, respectively. In addition, the incorporation of lignin improved the thermal stability of the composite film, and the maximal weight loss temperature was 313 ℃. Nanocellulose/lignin composite films show high application potential in the fields of food packaging, UV protection, and agricultural mulching films.