Abstract: To quantitatively obtain the deformation of microscopic fractures in shale during their initiation and coalescence, thus revealing the deformation evolution law and fracture mechanism of microscopic fractures in shale, this study explores and compares three micro-digital image correlation(DIC)strain characterization methods based on natural speckles, surface photolithography, and surface metal nanoparticle treatment of shale. The deformation evolution process during the initiation and propagation of microscopic fractures is investigated. The following conclusions are drawn: (1)All three surface treatment methods can be used for DIC deformation characterization. Utilizing natural speckles on the shale surface is relatively simple and convenient, but it cannot be used for deformation characterization at high magnifications. Photolithography is relatively inexpensive and does not affect the physical and mechanical properties of shale. However, the minimum speckle size is 2 μm, and the photoresist does not fracture with the microfractures of the shale, which can obscure the microscopic fractures. Surface metal nanoparticle treatment creates finer speckles with controllable speckle size, resulting in more accurate DIC deformation characterization. However, the shale needs to be treated at 300 ℃, which may affect its physical and mechanical properties. (2)The initiation and coalescence of discontinuous fractures are important forms of microscopic fracture propagation. Non-continuous strain concentration occurs before the formation of discontinuous fractures. Discontinuous fractures exhibit a hierarchical distribution, which may be the reason for the tortuous and complex nature of microscopic fractures. (3)Interconnected discontinuous fractures form the main fracture, while discontinuous fractures that are not connected to the main fracture close due to stress release, forming branch fractures. This study provides new technical means and research ideas for the characterization of microscopic deformation evolution in shale. It also provides experimental evidence for the study of microscopic fracture propagation and the formation and evolution mechanism of discontinuous fractures.