The temperature field of blast furnace tap hole clay was analyzed by using ABAQUS software. Samples taken from the tap-hole clay in depth of 1200mm, 2200mm, 2600mm and 2800mm after roasted for 100 minutes were studied by using XRD and SEM to investigate their roast mechanism and microstructure at different temperatures. The results show that the ore phase of the tap-hole clay in depth of 1200mm remained unchanged but only tar and asphalt appear the carbonation phenomena. There is a large number of SiC crystalline phase appears in depth of 2200mm. At the same time, porosity increases and coke structure is formed. The air permeability is enhanced. In the tap-hole clay of 2600mm～2800mm depth, elongated rod-likeβ-Si3N4 grains obviously increase while the SiC grains decrease. A large number of high-temperature flocculent mullite phase appears and the high-temperature strength of the tap-hole clay is strengthened.