In order to prepare poly (butylene adipate-co-terephthalate) (PBAT) foamed composites with low filling and high performance, rice straw fiber (RSF) was modified with phosphoric acid and melamine to obtain modified rice straw fiber (MPRSF). Then MPRSF and expandable graphite (EG) were ball-milled to prepare interfacial solder (EG-MPRSF), and EG-MPRSF@PBAT foamed beads were prepared by coating PBAT with EG-MPRSF. Finally, expandable graphite-modified straw fiber@PBAT (EG-MPRSF@PBAT) foamed bead composites were prepared by supercritical carbon dioxide (scCO2) and microwave sintering technology. Based on FTIR, XPS, SEM, EDS characterization and TGA, hardness, resilience and compressive strength test, limiting oxygen index test, vertical combustion grade test and cone calorimeter test, the effects of EG-MPRSF mass fraction (EG-MPRSF mass percentage of PBAT foamed bead mass, the same below) on the mechanical properties and flame retardant properties of the prepared EG-MPRSF@PBAT foamed bead composites were investigated. The results show that the EG-MPRSF@PBAT foamed beads composite can retain the original cell structure of PBAT foamed beads after sintering, and its hardness, resilience and compressive strength are greatly improved, and it has flame retardant properties. When the mass fraction of EG-MPRSF was 0.2%, the compressive strength, resilience and hardness of the prepared EG-MPRSF@PBAT foamed bead composites were 77.8%, 16.7% and 45.2% higher than those of the PBAT foamed bead composites without EG-MPRSF, respectively. The smoke production rate and total smoke production decreased by 14.9% and 24.8%, respectively, and the total heat release decreased by 17.1%.