Freezing and thawing effects on open-pit mines in cold areas are more unique; this is because the slope-shaping process of open-pit mines has a significant time effect; with the continuous descending and expansion of the rock layer, the initial small slopes are gradually developed into tall slopes with multiple steps, and at the same time, the slopes in the production process of open-pit mines with the cyclical temperature changes show a two-state cycle of freezing in winter and thawing in spring. The process generally extends from several years to decades [9] due to the freeze-thawing deformation of underground pipelines in Northwest China, freeze-thawing weathering of rocky cultural relics due to the different exposure times of the slope at different step levels and locations, the number of freeze-thaw cycles experienced is different. The degree of freeze-thaw damage to the rock body at each mine site is also different. Therefore, it is of great significance to study the rule of change of physical and mechanical properties of rock bodies in open-pit mines under the freeze-thaw cycle and to solve the unfavorable impacts brought by the freeze-thaw cycle for the safe and efficient production of open-pit mines. The change in rock's physical and mechanical properties under the freeze-thaw cycle is affected by multiple factors. At present, scholars at home and abroad generally divide the factors affecting the freeze-thaw damage of rocks into internal and external factors. Internal factors refer to the properties of the stone itself, including lithology [10], porosity [11], water content [12], and degree of fissure development [13]. External factors refer to the environmental parameters in which the rock is located, including temperature [14; 15], number of freezing and thawing cycles [16; 17], and hydrochemical environment [18; 19]. Many experimental studies have shown that the compressive strength, tensile strength, and modulus of elasticity of rocks are substantially reduced after undergoing multiple freeze-thaw cycles. The damage mode of rocks changes, and the reduction in rock physicochemical properties is even more significant in internal fissures or particular environments [20]. Whether affected by internal or external factors, the significant reduction in rock's physical and mechanical properties manifests its internal microstructural changes or damage. At present, scholars at home and abroad have studied the internal microstructural evolution law of freeze-thawed rocks mainly through nondestructive testing techniques, such as acoustic emission (AE) [21; 22], scanning electron microscopy (SEM) [23; 24], computed tomography (CT) [25; 26], and nuclear magnetic resonance (NMR). As a commonly used nondestructive testing technique in medicine, NMR technology has the advantages of fast detection speed and high accuracy. It is widely used in the analysis and detection of petrophysical tests [27; 28]. Porosity, free-fluid index, pore-size distribution, and permeability can be derived from NMR technology. However, NMR technology is primarily used in the study of freeze-thaw damage of concrete at present [29; 30], revealing that there is less research showing the microscopic damage mechanism of natural rocks under the freeze-thaw cycle conditions of open-pit mines. Therefore, this paper designs the freeze-thaw cycle test of mudstone in open-pit mines under the consideration of natural conditions, analyzes the change rule of mechanical parameters of mudstone freeze-thaw damage, and examines the change rule of mudstone pore structure and the superimposed effect of freezing, thawing, and hydration damages of natural mudstone under different conditions of freeze-thawing based on the NMR technology. Meanwhile, it probes the hydration mechanism of mudstone freeze-thawing injury.