Lignin was isolated from poplar sawdust through 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 show that the surface of the pure CNF film is smooth and dense, while the addition of lignin makes film rough with the increasing root mean square (RMS) roughness value from 19.8 nm to 62.7 nm. With the increase of lignin content, the tensile strength of the composite films is decreased from 140 MPa to 67.6 MPa. When the lignin mass fraction is 5%, the Young""s modulus is up to 7.11 GPa. In the meantime, lignin endows the composite films with excellent ultraviolet shielding properties with the UVA and UVB blocking rate of 99.23% and 100%, respectively. In addition, the incorporation of lignin improves the thermal stability of the composite films, and the maximal mass loss temperature is 313 ℃. The nanocellulose/lignin composite films show high application potential in the fields of food packaging, UV protection, and agricultural mulching film.