The invention discloses a direct shear testing device of saturated rock soil samples, which relates to the technology of mechanical strength test of rock soil. The structure of the direct shear testing device comprises a sample shear box, a loading system, a saturation system, a vacuum pump and a data acquisition system which are fixed on a frame to form a whole body, wherein the shear box is arranged in a water channel of the saturation system and guarantees the sample to be saturated completely, the loading system comprises a vertical loading system and a transverse loading system, the vertical loading system and the transverse loading system are respectively connected with the shear box and realize vertical loading and transverse loading of the shear box, the vacuum pump is connected with the saturation system and used for vacuumizing the closed water channel, and the data acquisition system is connected with the shear box and the loading system respectively and used for monitoring and recording the force and the displacement of the shear box. The direct shear testing device realizes direct shear tests of small-size and medium-size gravel soil, crack soil and soft rocks, and particularly can realize site tests of samples on the construction site and reciprocating direct shear tests of saturated rock soil.