In order to ensure that the sinter has good metallurgical properties and improve the permeability of the bed of material, the shape, length and growth law of the cracks in the material surface are analyzed, the causes of cracks and its relationship with ignition temperature are studied, an optical microscope is used to view the microstructure of the sinter at the cracks, and a mechanical analysis is given to the sinter at the cracks. The results show that in a certain range, with the increase of ignition temperature, the number of cracks tends to increase, but when the ignition temperature is greater than 1150 ℃, the number of cracks tends to decrease. With the increase of ignition temperature, the location of cracks gradually moves backward, that is, the higher the ignition temperature, the later the time of cracks. With the increase of ignition temperature, the mass fraction of FeO in sinter tends to decrease, but when the temperature exceeds 1150 ℃, the mass fraction of FeO in sinter tends to increase. There is a lot of needle-like calcium ferrite in the sinter at the crack, there are appropriate intergranular crevices and holes, the content of hematite is moderate, and the quality is better than that of the sinter inside. The occurrence of cracks can improve the air circulation in the bed of material, increase the permeability of the bed of material, and then improve the quality of sinter. The theoretical calculation results show that the repulsive force of the solid melt is greater than the gravitational force (F_引斥), and the strength of the solid melt is less than the surface tension of the liquid phase(ξ<ε_坚 , ν vertical), which is the necessary condition for the cracks to occur. The results can provide a theoretical basis for improving the actual sintering production.