Abstract: As a fundamental material in engineering construction, the study of crack propagation in rocks is crucial for ensuring the safety and stability of engineering structures. Sandy mudstone is selected as the study subject, and mesoscopic parameters are calibrated through discrete element numerical simulations based on laboratory uniaxial tests. Uniaxial compression numerical simulations are conducted on sandy mudstone to analyze the crack propagation and energy evolution characteristics during the failure process. The results show that: ①the numerical simulation results are in good agreement with the laboratory test data, and the mesoscopic parameters are reasonably set. ②Based on the changes in energy dissipation and crack quantity, the uniaxial compression process is divided into the compression stage, crack initiation stage, crack propagation stage, and post-peak failure stage. ③As loading progresses, the proportion of dissipated energy inside the sandy mudstone increases, crack growth rate accelerates, and cracks eventually gather near the macro failure surface, leading to the failure of the rock sample. Throughout the process, shear cracks dominate, and the angle of the macro failure surface is approximately 60°. ④Using the dissipated energy proportion （α） as an indicator, it is found that when α reaches 1.13%, 2.24%, and 10.81%, the crack propagation enters the next stage, and α=14.90% can serve as a precursor to the failure of the rock sample. This study quantifies the relationship between energy and crack propagation in rocks, and has certain reference significance for predicting the fracture of rock.