The invention discloses an assembling type in-situ direct shear test device for rock and soil, which belongs to the field of rock and soil testing, solves the problems that the existing in-situ sheardevice is large in volume, difficult to disassemble, difficult to operate, and has certain safety risks and the like. The assembling type in-situ direct shear test device for rock and soil comprises adirect shear box and a cover plate. The cover plate is located at the top of the direct shear box; the direct shear box is enclosed with a first steel plate, a second steel plate, a third steel plateand a fourth steel plate; pin holes are welded to corners of the first steel plate, the second steel plate, the third steel plate, and the fourth steel plate, respectively; a drag reduction sliding device is arranged on the top of the cover plate; a loading plate is arranged on the top of the drag reduction sliding device; a reaction jack is arranged on the loading plate; a reaction device is arranged on the reaction jack; and horizontal direct shear jacks are respectively arranged in center position of the direct shear box near the first steel plate and the third steel plate. The assemblingtype in-situ direct shear test device for rock and soil is suitable for field test, especially performs rock and soil in-situ direct shear test in a site restricted location.