This study performed a series of laboratory tests for understanding the role of heavy metal ions in the physical-mechanical behaviour.Different kinds of soils, including kaolinite, illite clays and sodium bentonite, were mixed with different concentrations of heavy metals Cu²⁺, Zn²⁺, Pb²⁺ to measure the changes in the Atterberg limits and the undrained shear strength.The testing results show that: the liquid limit and plasticity index of low active soils increase with the ion concentration, but sodium bentonite shows the opposite trend; the undrained shear strength of low-active soils increases with the ion concentration, but conversely for the high-active soils; based on the existing quantitative correlation between physical and mechanical properties of non-polluted soils, the quantitative relationship between the undrained shear strength and liquidity index of contaminated soils is investigated.It is found that the changes of undrained shear strength caused by adding heavy metal ions can be attributed to the corresponding changes in liquid limit and plastic limit.Such a result indicates that there is almost no chemical reaction caused by heavy metal pollution.The physical-mechanical quantitative relationship of heavy-metal-contaminated soils is consistent with the existing empirical relationship of non-polluted soils.