A CCD shooting system was applied to take the slagging images in a one-dimensional test furnace in order to analyze the problem of coal slagging. The thickness of the slag on the deposition probe was extracted through the image processing method, and the temperature distribution of the slag was obtained by the two-color method. Results show that the slagging growth process can be divided into different stages. Heat flux of the deposition probe is significantly different in different stages. The change of the slag thickness is a process that is from a rapid growth state to a steady state with small fluctuation. The temperature of slag surface which decreases from the outside to inside and shows a strong hierarchy can be seen by analyzing the slag’s temperature distribution in different time.