Abstract: The fluctuation behavior of welding arc affects the stability of welding process and the quality of weld formation. By the aid of high speed camera and image processing technology,a method of semi-quantitative characterization for the arc fluctuation range based on the arc image feature is proposed,and the influence of shielding gas flow rate on the arc fluctuation is investigated. The experiment and analysis results show that,under the influence of shielding gas flow,the arc fluctuation is mainly performed on the lateral（ direction of arc width） swinging,and the comprehensive arc fluctuation range decreases with the increase of welding current significantly,while the proportion of the lateral fluctuation rises. With the increase of shielding gas flow rate,the range of arc fluctuation goes up,and the arc fluctuation is more sensitive to the variation of shielding gas flow rate when welding with lower current. The research results can provide reference and basis for the choice of shielding gas flow rate in the actual welding process.