Abstract: In arc assisted activating TIG welding process, the base metal is pre-melted by an assisting arc along with mixture of argon and oxygen to form an oxide layer. After TIG welding, the weld penetration can be increased significantly. In this paper, two modes of uneven oxygen distribution at the surface of weld pool is proposed based on the experimental measurements; buoyance. A more sophisticated model of the weld pool in AA-TIG welding is developed, taking Lorentz force and surface tension into account. This model is developed to calculate the transportation hehavior of mass, momentum and energy in AA-TIG weld pool with the uneven oxygen distribution. In this paper, surface tension is a function of the temprerature coefficent and the concentration coefficient of the surface tension.The fluid flow in the weld pool is assumed to be turbulence and incompressible Newtonian fluid. The model is based on the RNG k-ε turbulence model. The experiments show that the calculated results agree well with measured value.