To investigate the influence of polymer material and contact surface roughness on the shear mechanical properties of soil-rock contact surface, we designed precast concrete samples as similar materials for rock surface and conducted a series of improved direct shear tests. The influence of organic polymer material and contact surface roughness was discussed. The improvement mechanism of polymer material was revealed by scanning electron microscope (SEM). Test results show that the polymer material could greatly improve the shear mechanical properties of the base soil and the contact surface by increasing the cohesive force, and the cohesive force of the substrate sample with 2% doping reached 41.76 kPa, which was increased by about 3 times. The cohesive force of different contact surface samples with 2% doping increased by about 2-7 times. The increase in the contact surface roughness could enhance the shear properties of contact surface by increasing the cohesive force, and the cohesive force of different contact surfaces with roughness of 6.5 mm increased from 12.27 kPa to 23.77 kPa, which was increased by 0.4-3.9 times. For flat contact surface and rough contact surface, the shear properties of polymer materials were strengthened in two different modes. The polymer material and the contact surface roughness had a synergistic strengthening effect on the shear properties of contact surface.