Abstract: Based on observation of scanning electron microscopy, three point bending cleavage fracture of 16MnR steel with coarse grain and coarse carbide was observed under different temperatures, and the style of crack origin of cleavage was analyzed. The results show that the types of crack origin were mainly carbide cracking on grain boundaries, inclusion cracking, interface separation of larger carbide, separation between spherical carbide and ferrite matrix and cracking of grain boundary in the experimental condition. The distance Xf between cleavage crack origin and plastic crack tip had a decisive effect on cleavage fracture and increased with temperature, and the Xf was not directly affected by the type of cleavage crack origin.