The application of ultrasonic vibration in the welding process can effectively suppress the pore defects of the weld. The different ultrasonic application methods own different effects on the weld pore. In this paper, the ultrasonic frequency vibration in the weld pool is ex-cited by the coupling of the ultrasonic frequency electrical signal and the welding electrical signal. The influence of ultrasonic excitation voltage and excitation frequency on porosity, number, location, and size of pore in weld was investigated. The results show that the variation of ultrasonic excitation voltage and frequency has a direct influence on the pore distribution. The pore defects can be decreased by the coup-ling of ultrasonic frequency electrical signal with reasonable parameters or increased by the coupling of ultrasonic frequency electrical sig-nal with unreasonable parameters. The ultrasonic excitation frequency is fixed at 30 kHz and the ultrasonic excitation voltage is changed. The porosity of the weld is close to that of the weld without ultrasonic action when the ultrasonic excitation voltage is 25 V and 75 V. The porosity of the weld is significantly lower than that of the weld without ultrasonic action when the ultrasonic excitation voltage is 50 V and 100 V. The ultrasonic excitation voltage is fixed at 100 V and the ultrasonic excitation frequency is changed. The porosity of the weld is the largest and exceeds that of the weld without ultrasonic action when the ultrasonic excitation frequency is 20 kHz. The porosity of the weld is lower than that of the weld without ultrasonic action when the ultrasonic excitation frequency is 25, 30, 35, and 40 kHz. The pores were mainly concentrated on the upper part of the weld and the number of pores of small size increased significantly after the coupling of an ultra-sonic frequency electrical signal, indicating that ultrasonic promoted the rise and escape of bubbles in the weld pool.