Carrageenan (KC), ammonium polyphosphate (APP) was compounded with four metal oxides (MO) Fe2O3, CuO, Al2O3, MnO2, respectively to obtain synergistic flame retardants (KC/MO/APP), thenNR/KC/MO/APP composites were prepared by adding KC/MO/APP into NR. The flame retardancy of the composites was tested by limit oxygen index (LOI),vertical combustion (UL-94) and cone calorimetry (CCT). The results showed that the UL-94 of NR/KC/MO/APP reached the V-0 level,and the LOI was between 26.5% and 27.3%,showing a good flame retardant effect.The peak heat release (pHRR) and total heat release (THR) of NR/KC/CuO/APP decreased by 63.7% and 42.0% compared with that of NR. At the same time,KC/MO/APP also has a smoke suppression effect, the total smoke release (TSP) of NR /KC/Fe2O3/APP composites is the lowest, which is 35% lower than that of natural rubber. Thermogravimetric analysis (TGA) test results show that the NR/KC/CuO/APP composite’s W800 reaches 34.85%, which is 28.7% higher than NR/APP. The analysis of residual carbon by SEM found that the carbon layer of the NR/KC/MO/APP system is denser, which shows that the synergistic effect of KC/MO and APP plays an important role in forming a stable carbon layer.Through DMA and mechanical property tests,it is found that the mechanical properties of NR/KC/MnO2 /APP are the best.Compared with NR/APP, the tensile strength and elongation at break are increased by 32.6% and 20.9%, this indicates that the addition of MnO2 can supplement the mechanical properties loss caused by the flame retardant to NR.