During the multi-wire GMAW, the working state of the arc will become unstable because of the arcs interference, which will affect the stability of welding process and welding quality. In this paper, the distribution of the electron temperature of the arc have been researched based on Boltzmann spectrometry. Electron densities under different conditions have also been calculated based on Stark width of the plasma spectrum. Combined with the analysis of high-speed photography, quantitative analysis of the arc interference can be obtained. For double wire case, the results of spectral diagnosis show that when the adding arc current is larger than the original arc, the temperature center of original arc is shifted to the new arc side, and the electron density of the original arc near new arc side is obviously increased. While the current of the new arc is equal to the original arc, the temperature and electron density distribution of the original arc all lead to the instability. In the case of triple-wire, the addition of the third arc causes the temperature distribution of intermediate arc become complex, and its electron density distribution is close to that of single wire case.