The invention discloses a multi-diameter rock core dual-ring direct tension rock tensile strength tester. The tester comprises three parts such as a loading system, a pressure monitoring and data acquisition system and a loading rack and sample clamping system. The loading system comprises an upper pressure disc, a ball head, a ball seat, a tower-shaped spring, a spherical hinge end cover, an oil cylinder, a lower pressure disc, a guide sleeve and a guide plate. The pressure monitoring and data acquisition system comprises a sensor and data acquisition subsystem, a pressure digital display screen, a monitoring compression gauge and a notebook computer data acquisition subsystem. The loading rack and sample clamping system comprises a diameter-variable rock sample inner ring pressure disc, a diameter-variable rock sample outer ring pressure disc, a lower crossbeam, stand columns, stand column fixed rings and an upper crossbeam. The tester can monitor and record the whole rock sample drawing damage test process, fast determine a tensile strength quantitative value in direct drawing of a rock, has a rigorous and reliable test principle and process and fill a gap in the research field at home.