Abstract: In order to understand the heat sources spatial distribution during high power laser-MIG hybrid welding of alu-minum alloy,plasma behavior was analyzed.A full factorial ex-periment with three factors and three levels was designed by tak-ing laser power,arc power and distance between laser beam and arc as factors.Combined with high-speed speed camera equip-ment and digital image processing technology,plasma dynamic behavior was observed and plasma geometric information such as width and area were extracted.Experimental results show that the plasma shape is the result of the couple of laser beam and arc.There is a certain threshold with the total power increasing,when the total power is lower than this value,the plasma size gradually decreases;when the whole power is over this value,the plasma size is expanded especially in high power situation.The distance between laser beam and arc obviously affects the plasma space distribution.Laser-MIG hybrid welding plasma ex-ists three steps-maintenance,expansion and recovery-repeat cy-cle during the distance between heat sources increasing.