Abstract: Thermal cycle experiments of laser welding with ultrasonic processing across different phases was designed, the analysis of the effect of ultrasonic vibration on welding thermal process showed that the influence of ultrasonic treatment to welding thermal process were mainly consisted of acoustic effect, heat transfer effect and mechanical stirring effect. The influence law of different ultrasonic vibration power to the characteristic temperature parameters includes welding maximum temperature, the heating speed, the high temperature residence time and cooling time was studied. By considering the root cause of the influence of ultrasonic treatment on welding thermal process the results show that the welding maximum temperature and the high temperature residence time both presented a trend that reducing first and then rising and reducing at last with the increase of ultrasonic power, meanwhile, the welding maximum temperature reached maximum when ultrasonic vibration power was 1200 W. The heating rate kept increasing trend with the increase of ultrasonic power, but the rate of increase corresponding to the different ultrasonic power were not identical, and the cooling time was kept decreasing.