Abstract: Conglomerate reservoirs attract widespread attention due to their abundant reserves and enormous development potential. However, existing studies show inconsistent results regarding the influence of gravel characteristics on mechanical behavior. This study conducted triaxial compression and CT scanning tests on core samples from the Mahu Sag. The tests examined the deformation, strength, and failure characteristics of the samples under varying burial depths and confining pressures. The results indicate that increasing confining pressure induces a brittle-to-ductile transition. The elastic modulus first increased and then decreased with increasing confining pressure, while Poisson's ratio exhibited a general upward trend. Mechanical parameters also varied among samples from different depths. Variations in elastic modulus and peak strength were primarily controlled by gravel distribution characteristics. The grain-size distribution of gravel critically influenced mechanical behavior: excessive distribution ranges promoted failure, small grain sizes induced large deformations, and moderate sizes and distributions required greater loading forces. Grain-size distribution also governed failure modes. Extremely small uniform grains or large heterogeneous grains generated circumferential failure around gravels, whereas large uniformly distributed grains produced predominantly transgranular failure; some samples displayed both circumferential and transgranular patterns. These findings provide essential references for the efficient development of conglomerate reservoirs.