An oxide scale layer is formed on the steel strip surface due to the high temperature (850-1100 degrees C) of the strip in hot rolling. The oxide scale layer may not be continuous because of the defects such as void existing in the layer before the strip enters the roll bite. The non-zero cracks may therefore be formed on the oxide scale layer, especially, when the oxide scale layer is relatively thick. These cracks may become narrower (even become closed) or wider (even form steel substrate extrusion) after hot rolling deformation. The development of the crack depends on the materials flow in the hot rolling process. The shape of the profile of the oxide scale layer has a significant effect on the materials flow in hot rolling process so it is important to investigate the effect of the oxide scale profile on the propagation of the crack. In this paper, the authors used the FEM method to simulate the crack propagation in oxide scale under hot rolling conditions for different profile parameters of the oxide scale layer. Simulation results indicate that the larger is the initial profiles surface roughness, the larger the crack width remained after rolling. With a rough profile and large initial crack width, the steel substrate extrusion may be formed.