In recent years, the safety of tailings pond has become a common concern by the local communities and governments. The stability of tailings dam can be increased by improving the mechanical properties of tailings. With the development of chemistry and chemical technologies, the stabilization of soil using polymer has become one of the hotspots in geotechnical engineering. However, few publications focus on studying the mechanical properties of polymer-treated tailings. In this paper, the polyacrylamide, sodium carboxymethyl cellulose, polyvinyl alcohol, and calcium lignosulfonate were used to improve the mechanical properties of tailings. And, the mechanical properties and microstructural characteristics of polymer-treated tailings were investigated. The direct shear test results show that the polyacrylamide has the best performance on improving the mechanical properties of tailings among the four polymers. The mechanical properties of polyacrylamide-treated tailings tend to be stable after 7 days of curing. With the increase of the polyacrylamide content, the shear strength of tailings increases. The cohesion increases first and then tends to be stable. The internal friction angle decreases first and then increases. When the polyacrylamide content is 0.3%, the triaxial compression test results show that the values of cohesion of tailings (tailings clay, tailings silt, and tailings sand) increase by 21.43 similar to 99.34%. The values of internal friction angles of tailings clay and tailings silt increase by 0.87 similar to 2.34%. But, the value of internal friction angle of tailings sand decreases by 3.77%. The SEM images and CT results show that the small particles are adsorbed together by polyacrylamide to form aggregate. The polyacrylamide can also form membrane structures on the surface of particles. These lead to the internal structure of polyacrylamide-treated tailings that is more uniform and dense.