Abstract: According to the assessment on stability of alu-minum alloy pulsed MIG welding,the analytical method was pro-posed based on the probability density of arc voltage signal.The ratio of first peak value and second peak value in voltage signal probability density distribution was taken as the criterion to as-sess the stability of pulsed MIG welding of aluminum alloy.The arc voltage signal probability density was calculated for 80 groups test and the ratio of two peak values in each group probability density distribution was obtained.Then a stability evaluation sys-tem for pulsed MIG welding of aluminum alloy was established.The result shows that the ratio is smaller,the stability is better,vice versa.