Abstract: Hollow probe is used to detect the plasma radiation of specific point passing the probe for spectrum collecting. The radiation of MAG and laser-MAG hybrid welding are collected with fiber spectrometer. The spatial distribution of the radiation is analyzed to compare the differences between welding process with and without laser hybrid. Furthermore, high speed video is also applied to study the coupling mechanics of laser-MAG hybrid. The result shows that a higher radiation intensity zone will be formed in the arc center. Beside the center zone, there is a somewhat lower radiation intensity zone. An 'ionized duct zone' will be formed near the laser focused point. The ionized duct is dominated by Fe fume. The ionized duct makes the welding arc more stable when the laser is applied. The higher radiation intensity zone changes the distribution of plasma energy, thus makes the energy focus on the arc center. The coupling effect of laser-MAG hybrid welding will form weld bead with deeper penetration than MAG welding.