Abstract: The mechanical properties of interbedded rock formations have a decisive impact on the safety of major engineering projects such as deeply buried tunnels and slopes. However, existing research has not yet established a comprehensive evaluation system, particularly regarding the strength evolution patterns and interbedding effect mechanisms of sandstone-mudstone interbedded rock formations. Taking sandstone-shale interbedded rock masses in tunnels as the research object, field sampling and uniaxial compression tests were first conducted to statistically analyze the strength distribution characteristics of sandstone and shale. Subsequently, a numerical model was constructed using FLAC3D, with the rock layer strength ratio as the core variable, to systematically conduct uniaxial and triaxial loading and unloading simulations. The research results indicate: Laboratory tests show that the compressive strengths of the two rock types exhibit significant fluctuations and both follow a log-normal distribution; numerical simulations reveal that as the strength ratio increases, the stress-strain curves of interbedded samples transition from a monotonically decreasing trend to a bimodal shape after yielding, with overall strength exhibiting a nonlinear increasing trend; when the strength ratio reaches 3, the interbedding effect is most pronounced, after which the increase in strength slows. This study clarifies the controlling role of strength ratio on the mechanical behavior of sandstone-mudstone interbedded rock, providing a theoretical basis for tunnel support design and stability evaluation, and offering important guidance for similar engineering practices.