Abstract: Poly (butylene succinate-co-terephthalate) (PBST)/ polyhydroxyalkanoates (PHA)/ lignin composite films were prepared by casting method. Fourier infrared spectroscopy (FT-IR), differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA) were used to characterize the structure, thermal properties, mechanical properties and crystallization properties of the composites. Results showed that no new chemical bond was formed in the melt blending process. The thermal stability of the composite materials had been improved. With the increase of lignin content, its mechanical properties first increased and then decreased. Under the condition of lignin mass fraction of 20%, the tensile strength and elongation at break could still reach 9.2 MPa and 848.0%. Moreover, the melt index and water vapor transmittance of the composite film could reach 15.6 g/10min and 31.6 g/(m²·d), respectively, which had excellent melt processing performance and water barrier performance. The composite films also had excellent UV blocking properties (UV absorption rate is greater than 99%), and could delay UV aging of the films. The results of soil degradation experiment showed that the degradation rate of the composite film could reach about 10% in 120 d, and the mechanical properties of the composite film decreased significantly. These indicate that the introduction of lignin could be rapidly degraded by microorganisms in soil, which could effectively accelerate the soil degradation of thin films. In conclusion, this method provides a scheme to improve the properties of polymers through melt blending and expands the application of lignin in multi-component polymer materials.