Abstract: The crack identification and extraction is the basis of understanding the evolution law of surrounding rock cracks. The existing methods for extracting stressed rock cracks based on visible light photos are poor in extracting the cracks of complex rocks (such as granite) composed of polychromatic minerals. In order to solve the problem, a method for extracting stressed rock cracks based on light reflectivity mutation is proposed. The method comprises four key steps of light reflectivity calculation, light reflectivity mutation point identification, light reflectivity mutation point space heterogeneity analysis and crack information extraction. The spatial differentiation of the mutation points of light reflectivity caused by crack growth is the key characteristic of crack identification. Therefore, the index-differentiation coefficient C, which reflects the concentration degree of spatial point distribution, is introduced. It is used to judge whether there is a crack in the digital image according to the spatial differentiation of the mutation points of light reflectivity. After the crack in the digital photo is judged, on one hand, the instantaneous information of the crack activity is reflected through the change speed of the light reflectivity, so as to study when and where cracks occur or expand in the specimen. On the other hand, the cumulative information of crack activity is extracted to analyze the development, propagation and penetration degree of rock surface cracks over a period of time. The experimental result shows that: ① The development and propagation of stress cracks in rock can cause the mutation of light reflectivity. The mutation speed can reach 0.2/s, which is much larger than the change speed (0.03/s) caused by other random factors. ② At the crack active time, the mutation point of light reflectance shows significant spatial differentiation (C value can reach 189), and the differentiation coefficient is much larger than that in random distribution (C value is 1). ③ The proposed method can extract the instantaneous information and cumulative information of crack activity. Finally, the reason for the change of light reflectivity during rock crack, the significance of rock mechanics of the proposed method and its application prospect in roadway safety inspection are discussed.