The microstructure and chemical composition of the burning-on layer of the directionally solidified blade of the DZ22B superalloy were studied by means of SEM and EDS. The results show that the metal ceramic like sand defects are formed by a part of ceramic particles covered during the infiltration of metal to shell surface pores. The main component of the burning-on layer composes fused corundum, with some interfacial reaction products containing Cr₂O₃ and HfO₂. According to the results of SEM analysis of blade cross section, the mechanism of the burning-on of the DZ22B directionally solidified blade is mainly caused by thermo mechanical permeation. A certain amount of burning-on inhibitor is added to the shell surface slurry, which significantly improves the penetration resistance of the fused corundum shell surface. The casting verifies that the surface of the DZ22B directionally solidified blade is smooth without burning-on, and the metallic luster on the blade surface is obviously observed.