A rock specimen, including a rock body. The rock body includes: an upper part, an upper end face, a first circular groove, a first cylinder, a first circular body, a lower part, a lower end face, a second circular groove, a second cylinder, and a second circular body. The first circular groove is disposed on the upper end face of the rock body and has a circle center coinciding with a center of the upper end face. A method for testing pure shear of the rock specimen, includes: 1) disposing the rock specimen on a test bench of a rock mechanics testing system, allowing the end face of the second circular body to contact the test bench; and 2) operating the rock mechanics testing system, loading a pressure on the rock specimen via the end face of the first cylinder and the end face of the second circular body.