Abstract: In order to reduce the internal damage of brown rice and the broken rate during the process of husking and whitening inside the machine, the formation and propagation mechanism of stress crack and influencing factors of brown rice being damaged and broken under impact were investigated. The experiments were carried out on different kinds of brown rice with different moisture content and impact momentum. The fracture surface of brown rice was observed by an INSPECT F50 scanning electron microscope, and the image processing and fractal dimension recognition calculation of the fracture surface of brown rice were carried out by Image J and Fraclac software, respectively. The relationships among moisture content, rice variety and impact momentum on the fractal dimension and critical crack propagation force of brown rice were studied. The experimental results showed that the formation and propagation of stress cracks in brown rice accorded with the fractal characteristics, and the fractal dimension can be used as an important parameter to characterize the internal damage and fracture of brown rice. Moreover, impact momentum was positively correlated with the fractal dimension and the critical crack growth force. In contrast, the moisture content is negatively correlated with the fractal dimension and the critical crack growth force. Therefore, lower moisture content and larger impact momentum would produce a larger fractal dimension of cracks and a lower critical crack propagation force in brown rice. In addition, the fractal dimension and critical expansion force of brown rice were also affected by brown rice varieties. The research results will guide for optimizing the basic theory of brown rice damage and breaking so as to improve the processing technology of brown rice.