The utility model relates to a tester for testing rock fracture toughness, particularly relates to a tester for testing rock fracture toughness under a confining pressure effect, and belongs to the technical field of geotechnical engineering. By adopting the tester disclosed by the utility model, a confining pressure exerting device is added to the original brazilian disk tester, the mode of simply and directly loading separation to carry out the test in the existing tester is changed, a spring locating device, a sealing device and a self-balance device are added to the box body; a dial indicator, an oil filling port, an exhaust hole and the like are matched, so as to record lateral and axial displacement change and control the liquid inside the box body to form stable confining pressure; the sample is fixed by using the spring locating device after the sample is put into the box body; a loading shaft can be prevented from being affected by confining pressure by adding the self-balance device, and control on loading of the sample is facilitated. By adopting the device, a splitting test of a rocker sample under the confining pressure can be achieved. Thus, the fracture toughness of the sample is calculated; the tester is reasonable in design, convenient to operate and use, and applicable to determination of the fracture toughness of kinds of rocks.