Abstract: The dynamic characteristics of keyhole in high power single beam laser and double beam laser welding of were studied. The test results show that the keyhole was always in the state of irregular cyclical fluctuations, compared with the process composed of formation, growth, maintained, shrink, annihilation in single beam welding, the keyhole in double beam laser welding also still exists the processes of separation and merging; Under same welding parameters and weld penetration, the fluctuation frequency of the single beam laser keyhole is about 1.5 times of that of the double beam laser, the mean value of keyhole opening area in double beam laser welding was about 2 times of that of the single beam laser, the fluctuation coefficient of variation of keyhole opening area was about 1/2 of that of the single beam laser.