High alumina refractory brick is one of the most widely used refractory bricks in the refractory industry. There are hundreds of specifications and sizes of high alumina bricks, which can be used in a variety of thermal kilns such as the steel industry, building materials industry, and power industry. Under normal circumstances, almost all the problems in the high alumina bricks will be exposed after firing, resulting in various defects. Among them, the main defects are under-burning, over-burning, damage, pollution, black core, distortion, cracks, and so on. Refractory manufacturers will separately introduce these defects and their characterization.