Abstract: Nano bentonite is a kind of new material, which is widely used in other industries, and has a great potential for application due to its rich resourses, low price and relatively mature production technology. This paper designed five groups of different dosage ratio of nano bentonite-red clay, and unconsolidated undrained triaxial tests under four different confining pressures were performed in each group respectively under the optimum moisture content of red clay. Finally, the effect of different content of nano bentonite on the mechanical properties of red clay was analyzed by the stress-strain curve. Thus we can get the law of shear strength and shear strength. The test results indicate that the addition of nano bentonite filled the pores of soil particles, which improved the mechanical properties of red clay. The optimum content is between 2%~3%,with the increase of the content of the red clay, the cohesion of the red clay increases at first and then decreases, while the internal friction angle of the red clay does not change. The test results indicate that the binding property of the main components of nano bentonite montmorillonite can increase the soil particle cement, and its expansive property is beneficial to filling the pore of the soil particles and its specific surface area can obviously enhance the mechanical properties of red clay.