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The behavior and emission spectrum of hybrid- welding arc plasmas are investigated in low-power YAG laser- metal active gas (MAG) arc hybrid-welding process, comparing with simple MAG welding case. The electron temperature and electron density of local arc plasma, deducing, respectively, from the Boltzmann plot method and Stark broadening mechanism, are analyzed in this paper. The conditions of local thermodynamic equilibrium (LTE) of arc plasma and self-absorption of emission spectral lines are discussed. The results indicate that laser- induced attraction and constriction of hybrid arc root are generated in low-power laser hybrid-welding process, and they make the synergy effect between laser and MAG arc increase. Comparing with simple MAG welding case, a zone above laser-heated spot with higher electron temperature and greater electron density is seen in hybrid-welding process. The maximal values of electron temperature and electron density of hybrid arc in this zone are about 1.56 plusmn 0.09 times 104 K and 1.61 plusmn 0.16 times 1017 cm-3, respectively. The welding arc plasmas are in the state of LTE, and none of the lines selected from emission spectrum of arc plasma is affected by self-absorption.