Abstract: To clarify the evolution law of sandstone pore structure under water pressure and reveal its dynamic change mechanism, an experimental study was conducted using nuclear magnetic resonance (NMR) technology. First, sandstone specimens with a size of 50 mm×25 mm were prepared and grouped; after pretreatment such as cleaning and drying, different water saturation pressures (5, 10, 20 MPa) and water saturation times (2, 4, 6, 8, 48 h) were set. Then, the NMR system was used to test parameters such as T₂ spectrum, porosity, and water content of sandstone under different conditions, and the variation characteristics of pore structure were analyzed. Finally, the variation law of T₂ spectrum was discussed from the perspective of physical mechanism, and its engineering application directions were sorted out. The results show that the amplitude of NMR T₂ spectrum signals varies under different water pressures; as the water saturation pressure increases, the T₂ spectrum curve shifts to the right with a decreasing shift amplitude, and the T₂ spectrum area is positively correlated with porosity and water saturation pressure but with a decreasing growth rate; the water content and pore volume of sandstone increase rapidly within t=0~4 h, and the pore structure tends to be stable after t≥6 h; under the same water saturation time, the increase in water pressure causes damage inside the rock, and after the pressure reaches 10 MPa, the pore structure becomes stable and the rock is completely damaged; the higher the water content of sandstone, the better the pore connectivity and the lower the strength.