Abstract: High in-situ stress, groundwater erosion and construction disturbance may affect the construction of tunnels in carbonaceous slate rocks. It is of great significance to analyze the relationship of microfissures from the view of meso-view. The carbonaceous slate samples were selected in the actual engineering site, and the backscattering analysis was carried out by scanning electron microscope (SEM) to determine the components of the samples. The X-ray diffractometer was used to analyze the mineral compositions and their contents were obtained by using the MDI Jade-6 software. The stress-strain curves of carbonaceous slate under different water contents were obtained by the uniaxial compression test under different water-cut conditions, and the deformation characteristics and failure law of each stage were obtained. The results show that there are mainly quartz, muscovite and albite in the carbonaceous slate, and the extremely complete cleavage of the carbonaceous slate is easy to form penetrating fissures, and the maximum strength of the carbonaceous slate is close to the elastic deformation before it reaches the peak strength. With the increasing immersion time, the stress-strain curve of the slate gradually becomes obvious in four stages, and the stress drop slows down after the peak value. The main mechanical characteristics are as follows: the intermineral structure is destroyed by water lubrication, water wedge action and latent corrosion. The elastic modulus and the uniaxial compressive strength of rock decrease significantly, and the Poisson's ratio and peak strain increase slightly. Macroscopically, the angle of fissures changes slowly.