During high-power disk laser welding, the surface of the weldment is gasified strongly by the laser irradiation. Meanwhile, the metal vapor plume is generated and changed into the plasma state. This plume can transmit through the laser beam reversely and has a significant shielding effect on the laser beam. Therefore, the laser power which should be transferred inside the weldment is decreased, the welding efficiency and welding quality are seriously affected. By studying and exploring the relation between the characteristics and variation rules of plume and the welding quality, the state of laser welding can be monitored in real-time by the plume characteristics. In the high-power disk laser bead on plate welding of a type 304 austenitic stainless steel plate at a continuous laser power of 10 kW, an extraviolet and visible sensitive high speed color camera is used to capture the metal vapor plume dynamic images. These digital images are transfered to the hue-saturation-intensity color spaces from the red-green-blue color spaces. Also, the area of metal vapor plume and the path length which the laser beam runs through the metal vapor plume are segmented and defined as the plume eigenvalues. The fluctuation of weld bead width is used to evaluate the stability of welding quality. By analyzing the statistics of the variance and mean values of plume eigenvalues, the experimental results confirm that the stability of the welding could be evaluated by the plume characteristics dynamically.