Abstract: The dynamic fluctuation behavior of the free surface of molten pool during pulsed twin wire GMAW was studied. Based on the two-dimensional wave theory, the transient mathematical model of the shock vibration of molten pool surface and the two-dimensional wave behavior resulting from it are established. The governing differential equation is derived. The corresponding initial and boundary conditions are given, and the numerical analysis is carried out by programming. The displacement and vibration velocity distribution of the free surface of the molten pool, the instantaneous fluctuation of the free surface of the molten pool under different droplet transition conditions and the interference caused by the surface fluctuation during welding are obtained. The results show that the surface wave mainly originates near the center of the front wire and the back wire, resulting in a strong depression on the surface of the molten pool. The welding wire with diameter of 1.0 mm can reduce the surface fluctuation of molten pool and prevent the occurrence of coarse weld ripple; When the droplet transfer frequency is 1 000 Hz, defects such as rough welding ripple and undercut are easy to appear. The fluctuation interference decreases with the decrease of droplet transfer frequency. The work in this paper can provide basic data and theoretical guidance for the industrial production of pulsed twin wire GMAW and the optimization of welding parameters.