The evolution of rock pore structure during the hydraulic fracturing process is highly complex, and quantifying changes in pore volume is crucial for understanding the mechanism of hydraulic fracturing. In this study, hydraulic fracturing experiments were conducted on rock cores using a self-designed experimental setup, and nuclear magnetic resonance (NMR) technology was employed to quantitatively characterize the evolution of pore structure throughout the hydraulic fracturing process. The results reveal that: (1) The pressure response of rocks during hydraulic fracturing is influenced by the injection rate and is correlated with the initial permeability of the rock core. Lower initial permeability results in a smaller response in pressure accumulation to injection rate, whereas higher initial permeability cores exhibit a significant response to injection rate variation. (2) Complete pore volume evolution during the hydraulic fracturing process was obtained through NMR. Changes in macropore volume dominate the variation in rock pore volume, with a significant increase observed with increasing injection rate. Moreover, this effect becomes more pronounced with a higher initial permeability of the rock core. (3) The fluid injected during the hydraulic fracturing process not only creates hydraulic fractures but also causes significant changes in rock pore volume, ultimately enhancing the initial permeability of the rock. The injected fluid causes changes in rock porosity and permeability. What is traditionally considered ineffective fluid leak-off in conventional hydraulic fracturing plays a crucial role in reservoir stimulation. The findings provide novel insights for further enhancing oil and gas recovery.