In order to investigate the effect of rock proportion on the progressive failures of soil-rock-mixture slope, five static overload tests are conducted on soil-rock-mixture slope with different rock proportion. In the course of the tests, the load and displacement of the load plate that acting on the top of the slope are measured. Meanwhile, the side slope is monitored by a high-definition image capturing system. The comparison of results between particle image velocimetry(PIV) analysis and the FLAC3D numerical simulation reveals the failure process of the slope under static overload., The PIV analytic results indicates that the rock blocks affect the shear band development. Through a comparison of PIV analytic results with different rock proportion, all the slopes develop Y-shaped shear band. As the rock proportion increases in the slope, on the one hand, the shear band affected by the gravel gradually shows deflection and twists, and two propagation modes are developed in the shear zone; on the other hand, the failure mode of the slopes gradually changes from general shear failure to local failure mode with rock proportion in range of 30%-53%.