Abstract: Based on the experimental time series of welding current produced by carbon dioxide gas metal arc welding (CO₂ GMAW)with short-circuit transfer under different welding speeds, the largest Lyapunov exponents of the welding sy stem are numerically evaluated using Takens' phase space reconstruction technique and the Wolf's algorithm for Lyapunov exponent.The results show that the largest Lyapunov exponent reaches small values when the welding processes approach high steady states.While the system is at the unsteady mode and experiences rapid variation, the largest Lyapunov exponent attains large values.So the largest Lyapunov exponent is negatively correlated with the welding process stability and can be taken as a novel indicator to quantify the process stability of CO₂ GMAW with short-circuit transfer.