The invention discloses an in-situ test device and method for testing the shear strength and long-term creep deformation of a rock sample. A test platform is cut in a region where the surrounding rockis located, and a shear rock sample, a flat surrounding rock surface and an upper surrounding rock are arranged on the surrounding rock; a horizontal shear box is arranged at the top of the flat surrounding rock surface and on a side of the shear rock sample; a horizontal shear device is arranged between the horizontal shear box and a side wall of the shear rock sample; a vertical load loading box is arranged on the lower end surface of the upper surrounding rock, and a vertical shear device is arranged between the lower end surface of the vertical load loading box and the shear rock sample;the horizontal shear device and the vertical shear device are of the same structure, and are powered by expanded cement slurry. The self-expansion property of the expansion agent is innovatively usedto provide a load source for in-situ shear test on site, and the expansion load is transmitted to the on-site rock sample through a loading probe of a dumbbell-shaped shear rod by means of expansion force generated by the expanded cement slurry to measure a shear strength index on a specific shear plane.