The variations in the electric property of loaded rocks are essential in understanding the rock dynamics and fracturing process. Decades of laboratory experiments have revealed different behaviors of stress-stimulated electric current due to the effects of rock types, loading modes, and detection methods. These different behaviors result in difficulties in revealing the underlying physics of electric current in rock and explaining adequately the wide variety of electric precursors measured before rock failure or geohazards. In this study, cubic- and conical-shaped diorite specimens were specially designed and produced to investigate experimentally the characteristics of pressure-stimulated rock current (PSRC) in the process of loading rock specimen to failure. We measured a particular phenomenon of diorite PSRC variation with pressure, that is, PSRC remained nearly stable until the applied stress reached 83%–98% of the failure strength. A remarkable step-like increment in PSRC was uncovered, and drastic oscillations with maximum amplitudes of several hundreds of nA happened one second prior to abrupt rock failure. A holistic mechanism that includes positive hole activation, field emission of electrons due to crack charge separation, and moving charged dislocation was applied to interpret this particular phenomenon. We found that these mechanisms contribute comprehensively rather than individually to the evolution of PSRC. We expect to provide an improved understanding of the underlying physics of PSRC and the variation in rock electric property.