To study the shear strength characteristics of unsaturated rubber silt mixtures, a series of direct shear tests was conducted on the rubber silt mixtures with different rubber particle contents and water contents. Based on the particle contact state theory, the meso contact mode of rubber silt mixtures was constructed, and the calculation method of rubber silt mixtures skeleton void ratio based on different rubber content was obtained. The test results show that the shear strength of rubber silt mixtures decreases with the increase of skeleton void ratio at a low water content, while the strength of rubber silt mixtures increases with the increase of skeleton void ratio at a high water content. Based on the soil-water characteristic curve of rubber silt mixtures, the corresponding relationship between matrix suction and water content is obtained. The shear strength of rubber silt mixtures increases with the increase of matrix suction at a low skeleton void ratio, and it exhibits decrease first and then increase with the increase of matrix suction at a high skeleton void ratio. Based on the influence of skeleton void ratio and water content on internal friction angle and cohesion, the shear strength development mechanism of unsaturated rubber silt mixtures was proposed, and the prediction formula of shear strength was established. The research results can provide theoretical support for the actual design and construction of rubber silt mixtures.