Abstract: As a phosphorous flame retardant, aluminum diethylphosphinate (ADP) can effectively improve the flame retardancy of natural rubber/butadiene rubber (NR/BR) materials, but it will have adverse effects on the mechanical properties of the materials. In this study, polydopamine/methyl methacrylate bilayer coated aluminum diethylphosphinate (PMMA-PDA@ADP) was successfully prepared by self-polymerization of dopamine hydrochloride under alkaline conditions. It was added to NR/BR to prepare NR/BR composites and the properties of the composites were tested and analyzed. The results showed that PMMA-PDA@ADP showed better flame retardant effect than ADP when the same amount of flame retardant was added. The LOI of NR/BR composite with 20 parts of PMMA-PDA@ADP reached 27.6%. The tensile strength of NR/BR composites increased by 7.7% compared with that of NR/BR composites with the same amount of ADP. This can be attributed to the improved flame retardant effect of the N and P co-effecting system composed of PMMA-PDA@ADP. Meanwhile, the compatibility between the flame retardant and NR/BR is improved by the organic coating structure, thus improving the adverse effect of ADP on the mechanical properties of NR/BR. This study provides an effective flame retardant modification method for NR/BR composites, which realizes the dual goal of improving the flame retardant properties of composites while improving the mechanical properties.