A large triaxial shear testing instrument for rockfill material degradation is characterized by comprising a test mainframe, a confining pressure and pore pressure servo loading system, a temperature control system, a closed loop measurement and control system and a computer control and data acquisition system (15). The large triaxial shear testing instrument for rockfill material degradation adopts a multichannel closed loop controller to realize two-way independent high-precision control for axial loading and lateral loading of a servo motor and a reducer ball screw, and a mechanical property test for a rockfill material under a complex stress path can be carried out; the large triaxial shear testing instrument for rockfill material degradation adopts a cold and hot control device provided with a temperature control pump, an acid-base circulating device and an anti-corrosion pipeline, so that physical weathering and chemical weathering tests can be performed simultaneously; and the large triaxial shear testing instrument for rockfill material degradation adopts a differential displacement sensor and a diameter deformation measurement sensor, and accordingly, accurate measurement of a dynamic size change process in a dry and wet change process of a rockfill material test piece is realized.