Abstract: The effect of Cu²⁺ on the variation of physical-mechanical properties of Guilin red clay is studied. XRD、XRF and mercury intrusion tests are carried out to investigate the variation law of main mineral components and the change trend of micro-pore structure in Cu²⁺ contaminated red clay. The results show that the main mineral components in red clay are kaolinite, quartz and goethite. Cu²⁺ pollutant has a significant impact on the content of these three main mineral components. With the increase of Cu²⁺ concentration, the content of kaolinite and goethite gradually decrease, while the content of quartz gradually increases. The change rate of content is kaolinite>goethite>quartz. When the Cu²⁺ concentration is 2%, the content loss rate of kaolinite and goethite are as high as 10.69% and 5.38%, respectively. The pore distribution curve of red clay is bimodal. The double peaks are distributed between 0.01~0.1 μm and 1~10 μm respectively. The micro-pores between 0.01~0.1 μm account for the absolute advantage. With the increase of Cu²⁺ concentration, the "double peak" move to the right gradually, and the pores become larger, the "peak width" widens gradually, and the pores become more numerous. A series of tests are conducted to observe the variation law of the deformation strength characteristics of red clay contaminated by Cu²⁺. They include unconfined compressive strength test, direct shear test and compression consolidation test. The results show that Cu²⁺ contamination has a significant effect on the deformation strength properties of red clay. With the increase of Cu²⁺ concentration, the unconfined compressive strength, shear strength and its index(C, φ) of the red clay decrease gradually, the initial void ratio e₀ and the compression coefficient α increase gradually. When the Cu²⁺ concentration increases from 0 to 2%, the unconfined compressive stress-strain curve of soil changes from typical strain softening type to weak strain hardening one, the peak value of unconfined compressive strength decreases by 76.91% and the average loss rate of shear strength reaches 69.36%.