Abstract: In order to evaluate the stability of aluminum alloy pulsed MIG welding,an approximate analysis has been done on voltage signal in the process of aluminum alloy pulsed MIG welding.The calculation and comparison of the approximate entropy on voltage signal under different welding procedures such as welding speeds,wire feed rate,duty cycle and so on,show that,the approximate entropy of voltage can reflect the stability of the process of aluminum alloy pulsed MIG welding.The results show that,the smaller the average value of approximate entropy and standard deviation is,the more stable the welding process will be.On the contrary,the welding process is unstable while the average value is high.