Soil-bentonite barrier is one of the most important means to isolate contaminated sites, which has been widely used in engineering practice. Adding hydroxypropyl methylcellulose (HPMC) to the soil-bentonite barrier can effectively make up for the attenuation of its anti-seepage performance in heavy metal environment. A series of experiments including free expansion, scanning electron microscope, permeability, one-dimensional compression and direct shear strength for the destruction of bentonite structure by copper ion, the improvement mechanism of HPMC and the barrier mixing HPMC with different ratios are conducted under high ion concentration (50 mmol/L) environment. The results show that HPMC can reduce the agglomeration of copper contaminated bentonite, keep the continuous structure of bentonite and as HPMC mixing ratio increases, the damage degree of barrier gets lower and the anti-seepage performance becomes better. The mechanical properties of barrier such as the compressibility increases, but shear strength decreases slightly with higher HPMC mixing ratio.