Abstract: 6061 aluminum alloy weld with good appearance was obtained by using fiber laser. The spectrometer and high-speed camera were applied to acquire plasma spectrum and dynamic image respectively, the plasma spectral characteristic was analyzed, and the correlation between spectral intensity with its fluctuant degree and the location of porosity with its percentage were discussed during laser deep penetration welding of the aluminum alloy. The result shows that the degree of plasma ionization is low, and there is only metal atomic spectral lines during the laser deep penetration welding of aluminum alloy. The intensity of AlI 396.152 nm spectral line can indicate the plasma spectral characteristic of welding process. There is not the necessary relationship between the intensity of plasma spectrum with its degree and the location of hydrogen porosity with its percentage in aluminum alloy weld. Furthermore, there is no correlation between the intensity of plasma spectrum and the location of keyhole porosity, but the fluctuant degree of plasma spectral intensity can indicate the percentage of keyhole porosity.