Abstract: Salt will weaken the strength of soil, resulting in soil deformation. In order to explore the influence law of different concentrations of NaCl solution on crack development of red clay and its engineering properties, mud samples with different concentrations of NaCl were prepared respectively. We regularly weighed and took photos of the samples, and observed the development process of the sample crack. The results showed that the increase of NaCl concentration changed the interaction force between soil particles, and the water evaporation rate of red clay and the number of crack blocks decreased obviously. NaCl solution distinctly inhibited the crack development of red clay, the higher concentration is, the more obvious of inhibition is. In addition, the influence of different concentration of NaCl solution on the mechanical properties of red clay was explored through the limit moisture content and direct shear test, and the change reason of mechanical properties and the rule of crack development were analyzed by Zeta potential test. It was found that the friction between soil structure and particles was changed by NaCl solution, which reduced the thickness of diffusion layer, so the liquid and plastic limit and shear strength index of red clay decreased with the increase of solution concentration.