The work aims to solve the problem that traditional petroleum-based composites are difficult to be degraded and recycled, causing serious environmental pollution and resource waste. In this study, the dealkalized lignin, a by-product of papermaking process, was nanosized and dispersed as a filler into a PVA/Bta (polyvinyl alcohol/ betaine, PALB) polymer matrix composed of polyvinyl alcohol (PVA) and betaine (Bta), and then used to prepare composite film materials by the solution casting method. N-lignin nanoparticles (NLNPs) prepared by nanoprecipitation had the advantages of small particle size, uniform particles and stable storage property. Therefore, the prepared NLNP/PALB composite film material had a mechanical strength of 105 MPa and a tensile strain of 385% and also had excellent UV shielding efficiency and excellent thermal stability. Based on the excellent properties, the composite film is expected to be applied in environmentally friendly food packaging and other fields.