Red clay is a typical special soil, and its characteristics of swelling in water and shrinkage in water loss will have a great impact on the stability of red clay foundation and subgrade. In order to further understand the physical and mechanical characteristics of red clay, the relationship between shear strength and water con- tent of remolded red clay in Jiangxi province is studied experimentally in this study. The indoor direct shear test results show that with the increase of water content, the shear strength and cohesion of red clay decrease, the variation curve of cohesion and water content is similar to " S" type, while the internal friction angle fluctuates within a certain range, and the influence mechanism is more complex. According to the analysis of X-ray diffraction test, the mineral composition of Jiangxi red clay mainly includes Shi Ying, mica, potash feldspar and a small amount of iron oxide as cementing material. Through scanning the soil sample with electron microscope, it is found that the microstructure characteristics of red clay have changed greatly after shear failure, which indi- cates that the change of microstructure of red clay after shear makes the soil deformed or even destroyed.