The strength of frozen coarse-grained soil is critical in the construction of infrastructure and urban underground spaces in permafrost regions. For the investigation of frozen coarse-grained soil strength characteristics, combining the discrete element method (DEM) with experiments is expected to yield superior results. Simulations can reduce experimental workload and reveal the microscopic mechanical behavior of frozen coarse-grained soil. However, current DEM software for soil specimen generation often results in nonuniform gradation, leading to biased results. So the present study proposes a gradation-dependent specimen generation method, ensuring high consistency between generated and actual specimen gradation. Uniaxial compressive strength (UCS) tests on frozen coarse-grained soils are conducted by varying temperature and gravel content. Based on the test results, the UCS and stress-strain relationship of frozen coarse-grained soil is simulated using the specimen generation method, and the microscopic parameters are calibrated accordingly. Then a relationship between microscopic parameters and temperature is established to predict the UCS of frozen coarse-grained soil at various temperatures, with validation through actual tests. Finally, based on the simulation results of uniaxial compression tests, particle displacement, force chains, and bonding states during different strains on frozen coarse-grained soil are analyzed to reveal microscopic strength failure mechanisms. The results enhance understanding of the mechanical properties of frozen coarse-grained soil, provide parameters for engineering designs in permafrost regions, and offer computational methods for high-precision numerical simulation studies.