Abstract: Laser-MAG (Metal active gas arc welding) hybrid welding process was adopted. Based on surface appearance of weld, longitudinal section morphology and penetration fluctuation degree of weld, high-speed camera system and image processing method were used to characterize and quantify two key process information, spatter and plasma in welding process. Relationship between key characteristics and stability of welding process was systematically studied when laser power was increased from 5 kW to 30 kW. The results showed that with the increase of laser power, surface appearance of weld appeared a periodic “convex-concave” phenomenon, and internal cracks and penetration of weld also changed periodically. With the increase of laser power, both plasma area and spatter area increased, and whose fluctuation degree and penetration fluctuation degree were all positively correlated. The increase of plasma area would lead to intensification of energy attenuation during laser transmission, and the increase trend of weld penetration would gradually slow down, whose fluctuation degree was one of the key factors affecting stability of welding process.