Using a special impulse device, the impulse electroless Ni-P alloy plating were prepared. The microstructure, crystallization and the starting activation energy for crystallization was investigated by TEM, XRD and DTA, compared with electroless Ni-P alloys plating. The results showed that the diffractive ring was wider when using impulse, depositing temperature dropped up to 65 degrees C,and crystallization temperature rose up to 310 degrees C. Furthermore, the starting activation energy for crystallization and crystallization temperature of impulse electroless Ni-P alloys plating measured were more than that of electroless plating in the heating rate at 5, 10, 20, 40K/min, and it was also higher in the amorphous disorder degree and the starting crystallization temperature. Impulse electroless Ni-P alloys plating had better performance of thermal stability.