In this account, the interaction between E44 and KH560 modifiers and poly(butylene succinate)‐distillers grains (PBS/DGs) composite system was studied experimentally and theoretically by means of molecular dynamics simulation. The PBS/DG biodegradable composites were prepared by melt blending the modified DG and PBS, and composting degradation tests were carried out for a period of 75 days. The effect of E44 and KH560 modifiers on the interfacial features, tensile characteristics, thermal stability and degradation properties of PBS/DG composites were examined. The results showed that both χ and Emix significantly decreased in the composite system, indicating that PBS and DG became easier to mix together in presence of E44 and KH560. Also, the interface effect of DG and PBS improved after the modification with KH560. The mechanical properties of the composites remarkably enhanced when DG was treated with 2% KH560. When compared with PBS, the tensile strength and elongation at break were boosted by 23.66 and 33.18%, respectively. After composting degradation for 75 days, the mass loss rate of PBS/DG reached 42.82%, corresponding to 5.90 times higher than that of pure PBS. Overall, the comprehensive properties of the composites improved. POLYM. COMPOS., 40:1499–1509, 2019. © 2018 Society of Plastics Engineers