Abstract: Rock-soil aggregate is a special kind of engineering geological body. The type and content of soil or rock can influence the shear failure characteristics of the mixture. Since the mechanism of shear failure is not clear enough, it is difficult to determine the strength parameters of such fillers. Twelve in-situ push shear tests were carried out on the pelitic shale-silty clay mixture in order to further ascertain the rock-soil mixture shear failure characteristics, and some significant results were obtained. Through the in-situ tests, the complete load-displacement curves can be divided into five stages. Meanwhile, the 3D grid graph of the shear failure surface was obtained to establish the foundation of further research on the internal failure mechanism of rock-soil mixture.