Abstract: The heating of the weldment, the protection of the end face, the removal of oxides and dirt during the rail flash welding process are all caused by the formation and blasting process of the liquid bridge. This paper analyzing the evolution behavior of the liquid bridge during the welding process plays an important role in understanding the rail flash welding process and further studying the welding heating and protection mechanism. Through the flash welding test of specially designed rail joints and conventional rail joints, the liquid bridge formation and blasting process images of rail AC flash welding process were collected by high-speed photography, and the obtained graphics were calculated and analyzed. The research results show that the formation and blasting time of the liquid bridge is millisecond, which will generate a large amount of high-pressure metal vapor beneficial to the end face protection and liquid bridge blasting, and the high temperature metal jet velocity after blasting can reach more than 90 m/s; During the formation and growth of the liquid bridge, there will be dynamic movement on the rail end face that will affect the uniform heating of the rail end face. The liquid bridge blasting is not at the initial formation position of the liquid bridge; During the welding process, the melt can appear the phenomenon of "secondary explosion"; Not only can the rail at the moving end form a liquid bridge, but also the vibration of the molten metal layer at the end is conducive to the formation of a liquid bridge.