In this paper，electroless Ni-P plating on copper substrate at 50 °C in ultrasonic field was carried out. The frequency of ultrasonic waves was 40 kHz. The effect of ultrasonic on the composition, plating rate and morphology of Ni-P deposite was investigated at the ultrasonic power of 40, 70 and 100 W. The experimental results showed Ni-P deposit could not be obtained without ultrasonic field at 50 °C. The content of nickel and the thickness of Ni-P deposit increased with the ultrasonic waves power increase. Ultrasonic irradiation power remarkably refines the nodule size of Ni-P particles. The collapse of cavities in solution seems to suppress the Z-direction growth of the nodule.