<p>The instability of soil slope boulders represents a prevalent geological hazard, characterized by its sudden onset and significant threats to engineering safety. However, the burial depth of boulders, a critical parameter for stability assessment, poses challenges for direct measurement. To facilitate rapid and accurate stability evaluations, this study introduces a method for assessing soil slope boulder stability based on natural vibration frequency. By simplifying the interaction between the boulder and the surrounding soil into a multi-degree-of-freedom spring-mass vibration model, we derive a dynamic characteristic model for the boulder. This model integrates the Limit Equilibrium Method with the dynamic framework to establish a stability evaluation model predicated on natural vibration frequency. The study identifies two primary failure modes for boulders: shear-sliding and rotational-toppling types. Utilizing the proposed model, we elucidate the quantitative relationships among natural vibration frequency, boulder burial depth, and boulder mass. Experimental investigations with boulder models of varying sizes demonstrate a nonlinear relationship between natural vibration frequency and both burial depth and mass. By combining the model with the Limit Equilibrium Method, we derive a formula for calculating the safety factor, which is validated through engineering case studies. The findings reveal that the calculated safety factor agrees well with numerical simulation results, thereby confirming the model’s applicability in practical engineering contexts. This study establishes a robust theoretical framework for monitoring and preventing geological disasters associated with the instability of boulders on soil slopes.</p>