Abstract: Natural rubber (NR) and butadiene rubber (BR) have a wide range of applications, but their limiting oxygen index (LOI) is only about 19% and they are easy to burn. Diethyl aluminum phosphate (ADP) can improve their flame retardancy, but the efficiency is not high and it can easily lead to a decrease in the physical and mechanical properties of the rubber. In this study, a complex formed by copper ions and cysteine (Cys-Cu) was compounded with ADP to form different proportions of composite flame retardant CCA, which was added to the composite rubber (6N4B) system of natural rubber and butadiene rubber. The results showed that the LOI values of the composite rubber with 15 parts of CCA flame retardant were all increased. Cone calorimeter test showed that the peak heat release rate (pHRR) and total heat release (THR) of 6N4B-5 decreased by 51.4% and 14.9% respectively compared to the composite rubber without flame retardant. The dehydration of phosphate groups and the catalytic effect of copper ions made the composite rubber have good flame retardant properties, which were significantly better than those of the composite rubber with only ADP. More importantly, the vulcanization performance and mechanical properties of the rubber composite system with CCA have been improved. This study provides a new strategy for effectively improving the flame retardancy, vulcanization characteristics, and mechanical properties of NR/BR composite rubber.