To explore the mechanism of damage and deterioration of fractured rock mass under the coupling effect of freeze-thaw and load, triaxial compression tests were conducted on rocks with different crack lengths and freeze-thaw cycles. The indoor test process was reproduced using PFC3D numerical simulation software and the reliability of the simulation was verified. The results show that during the freeze-thaw process, the relative content of small pores first increases and then decreases, while the relative content of large pores shows a trend of first decreasing and then increasing; The effect of confining pressure and prefabricated cracks on the mechanical properties of rock samples is opposite. The weakening effect of prefabricated cracks of 10 mm, 20 mm, and 30 mm on the bearing capacity of red sandstone is 25%, 66%, and 80%; The freeze-thaw cycle leads to the expansion of microcracks in the rock sample, making it easier to converge at the prefabricated cracks under confining pressure. The failure mode of the complete rock sample changes from tension to shear, and as the confining pressure increases, the fractured rock mass exhibits a shear failure mode, and the length of the cracks does not change the failure mode of the rock mass; By introducing the volume constitutive equation of water particles changing with temperature, the entire process of indoor freeze-thaw cycle test damage is reproduced. After 40 freeze-thaw cycles, the interior of the rock is fully damaged, and the number of cracks increases exponentially; PFC3D calculation shows that the failure point of the complete rock sample first appears at the loading point, while the fractured rock sample first appears at the loading point and the prefabricated crack. The overall crack curve presents an "S" shape, which can be divided into three stages: gentle, steep, and gentle. The longer the prefabricated crack length, the greater the damage to the rock sample, leading to a weaker ability of the rock sample to resist failure. The three-dimensional numerical simulation reflects the fracture behavior of freeze-thaw fractured rock mass, which can provide a basis for studying the evolution law of rock mass fracture in mining engineering.