Abstract: Acquiring the basic data of the surface tension of molten metal under welding condition is of great significance for understanding the physical mechanism of weld process,such as metal flow behavior, heat transfer mechanism and defect formation.However, real-time measurement is very difficult. The oscillating frequency of weld pool in 304 stainless steel with single component (TiO₂ ,CaF₂ ) and two component (30%TiO₂ + 70%CaF₂ , 70%TiO₂ + 30%CaF₂) activating fluxes was measured by laser-vision method. According to the analytical model of the characteristic frequency and surface tension of the molten metal in a specific mode the surface tension of the molten metal was calculated. The influence of different components of the activating fluxes on the average surface tension of the molten metal is analyzed. Experimental results revealed that TiO₂ activating flux can convert the surface tension gradient and change the flow direction of the molten metal. CaF₂ activating flux can reduce the absolute value of surface tension and increase the flow velocity of the weld pool. The increase of penetration in two component activating flux is the result of the combination of the increase of the flow velocity of the weld pool and the change of surface tension temperature gradient.