In order to improve the effectiveness of mechanized walnut shell breaking, a mechanical method was adopted to break Wen 185 walnut shell, and the scanning microscopy (SEM) was used to observe the fracture of the walnut shell. The characteristics of the walnut brittle fracture were investigated based on the theory of brittle fracture. The results showed that the walnut shell consists of two layers because its cell fracture revealed different patterns; the cells in the outer layer had small dimension and large density while the cells in the inner layer were just the opposite. The outer region was about 2 times as thick as the inner region. The morphology of the walnut shell fracture in different parts was similar, with natural shell ditch marking, cracks, impurities, holes and other crack features. These features were the cause of the walnut shell crack under load. Exerting shock loads on ends and transverse abdomen of the walnut shell could increase the broken rate of part of walnut shell. Moreover, walnut shell and kernel were separated much more easily.