Arc equivalent resistance signal of aluminum alloy twin-wire pulse metal insert gas（PMIG） welding was decomposed to several intrinsic mode functions（IMF） by variational mode decomposition（VMD）. Each IMF contains the characteristics of the original signal in its own frequency

which can reconstruct the original signal completely and separate the noise effectively. And the singular spectral of the characteristic mode matrix formed by the IMFs was calculated

then

according to the theory of information entropy the singular spectral entropy was obtained. Here the arc equivalent resistance VMD-singular spectral entropy method was proposed to evaluate the stability of aluminum alloy twin-wire PMIG welding

and a series of experiments were carried out with the same current and voltage parameters and other different conditions to test the effectiveness of the method. The results show that the more stable the welding process is the greater the VMD-singular spectral entropy will be

and it can soundly measure the stability of aluminum alloy twin-wire PMIG welding.