Abstract: For the molten pool behavior in K-TIG welding, the Level-Set method was used to track the changes in the free surface of the molten pool, and a two-dimensional transient numerical calculation model for stationary welding was established. The influences of buoyancy, electromagnetic force, arc pressure, plasma flow shear force, and surface tension on the molten pool behavior were investigated. The results show that when the buoyancy, plasma flow shear force, and Marangoni force with a negative temperature coefficient of surface tension (∂σ/∂T < 0) act individually, an outward flow forms inside the molten pool; whereas when the electromagnetic force and Marangoni force with a positive temperature coefficient of surface tension (∂σ/∂T > 0) act individually, an inward flow forms inside the molten pool. The flow velocities in the molten pool under the individual actions of plasma flow shear force and surface tension are of the same order of magnitude, but the flow velocity under the action of surface tension is higher. In comparison, the buoyancy, electromagnetic force, and arc pressure have a smaller effect on the convection in the molten pool, among which the arc pressure has the smallest effect. When the buoyancy, electromagnetic force, and Marangoni force with ∂σ/∂T > 0 act individually, the surface of the molten pool slightly bulges. When the plasma flow shear force, Marangoni force with ∂σ/∂T < 0, and arc pressure act individually, the surface of the molten pool exhibits concave deformation, and the maximum concave deformation occurs under the action of arc pressure. The simulation results agree well with the experimental results, verifying the accuracy of the model.