Based on the approximate entropy theory and related algorithm, approximate entropy analysis of current in short-circuiting arc welding in CO2 shielding gas are performed from the point of view of nonlinear time sequences. Calculation and comparison of approximate entropy of current under different wire-feeding speeds, setting voltages and different gas flow rates show that approximate entropy of current can be taken as a creterion of stability of short-circuiting transfer. The results show that greater approximate entropy and less fluctuation indicate a more stable welding process.