A flame retardancy PA66 resin is prepared by the reaction between hexamethylendiamine and 2,2-(amino acid-phenyl phosphine oxide) propane (BNNPO) synthesized in the lab. The Fourier transform infrared spectroscope (FTIR) results reveal that BNNPO contains N-P groups. The thermogravimetric analysis (TGA) results show that BNNPO possesses significantly the thermal stability. Meanwhile, the FTIR results reveal that BNNPO is grafted in the main chain of PA66 successfully. Compared with the pure PA66, the flame retardancy PA66 is provided with excellent thermal stability by TGA results. The limiting oxygen index (LOI) and UL-94 test results of flame retardancy PA66 reach to 28% and V0 respectively when the content of BNNPO prepolymer reaches to 4.5 wt%. The flammability and flame retardancy mechanism of flame retardancy PA66 resin are also studied by the cone calorimeter and the scanning electron microscope (SEM) respectively. The mechanical property results show that the flame retardancy PA66 resin keeps the favorably mechanical properties when introducing BNNPO.