Using the mixture of waste tires and soil as building materials in the field of civil engineering is one of the most promising measures to deal with waste tires. In order to study the effect of waste tire rubber particles on improving silt, taking the mixed soil of rubber particles and silt as the research object, the soil-water characteristic curve of rubber silt was measured by filter paper method, and the effect of different moisture content and rubber content on the soil-water characteristic curve was analyzed. The results show that at the same rubber content, the matrix suction of the mixed soil decreases nonlinearly with the increase of moisture content, showing a typical three-stage characteristic; at the same moisture content, the matrix suction increases at first and then decreases with the rubber particle content. When the rubber content is 20%, the matrix suction of the mixed soil is the largest. The soil-water characteristic curve model of mixed soil is established based on the Van Genuchten model. Based on the particle contact theory and considering the different specific gravity of particles, the contact state model of mixed soil is established, and the skeleton void ratio is constructed to describe the unsaturated characteristics of mixed soil. the matrix suction of mixed soil increase at first and then decrease with the increase of the skeleton void ratio.