The invention relates to an angle-variable subzero-temperature direct shear apparatus for rock and a test operation method, belonging to the technical field of equipment for rock mechanics testing. The angle-variable subzero-temperature direct shear apparatus comprises a host framework, a vertical loading mechanism, a vertical load support mechanism, a horizontal loading mechanism, a horizontal load support mechanism, a shearing box, a temperature control system, a measurement and control system and a computer system. The shearing box is arranged in an insulation can of the temperature-control system and realizes a subzero-temperature testing environment; the shearing box comprises a shearing box body, an arc slide rail, a rotating member, a wing-shaped fixture block, a semi-circular guide groove plate, a middle separator plate, a swivel positioning mechanism, and front and back end caps; and the shape of the shearing box is maintained unchanged while the internal structure of the shearing box changes from time to time through simple operation, so the purpose of shearing rock samples with different-angle cracks is achieved. The direct shear apparatus for rock and the test operation method can effectively overcome problems in subzero-temperature and angle-variable shearing; and the direct shear apparatus is simple in the principles of the overall structure, convenient to operate, high in visualization degree, changeable in functions and good in applicability.