Abstract: The force and critical sizes of metal droplet should be investigated in order to realize controlling in the free metal transfer in the CO₂ arc welding. Therefore,under the precondition of repulse force,gravity and surface tention,the numerical simulation model of free droplet of the CO₂ arc welding based on Surface Evolver is established. The free metal transfer is analyzed according to the principle of the minimum energy of a system. In addition,the effect of repulse force on the metal transfer is investigated and the connection between welding current and critical sizes of the droplet is acquired preliminarily. The investigation lays the basis for controlling the free metal transfer under low current in the next step.