A novel preparation of halogen-free flame retardant aluminum phenylphosphinate ( BPA-Al ) was studied by dichlorophenylphosphine and aluminium sulfate octadecahydrate under aqueous phase. The molecular structure of sample was characterized by 1H NMR, 31P NMR, FTIR and ICP. Under the optimal reaction conditions, the yield of BPA-Al was up to 89.6 %.Thermal stability of the products was investigated in detail by TG-DTA, which could meet decomposition temperature of the excellent flame retardant. The application of BPA-Al to Nylon 6（PA6）was investigated. The content is 10 %, the LOI to 30% and UL94 V- 0, the flame retardant of PA6 has been significantly enhanced. And it is also good mechanical properties, the tensile strength to 84.9 kPa.