Abstract: The variation in particle gradation of the rockfill material used for dam construction significantly affects its mechanical properties, thus influencing the stability and safety of the rockfill dams. Mechanical property tests of the upper envelope, the average and the lower envelope of the particle gradation were conducted on the rockfill materials from the upstream and downstream zones of a certain rockfill dam, with upper bound, average, and lower bound gradation curves analyzed pre- and post-testing. Results indicated that under the same sample preparation power, as the gradation shifts from the upper bound to the lower bound, the porosity of the rockfill material increases, while the strength parameter φ and the Duncan-Chang model parameter K decrease. This suggests that with a reduction in fine particle content, the compaction level and mechanical performance of the rockfill material decline under constant power. The poorer the parent rock quality, the higher the particle breakage rate, leading to a diminished impact of initial particle gradation differences on the mechanical properties post-compaction. Dam construction of rockfill dam should thus place greater emphasis on the influence of gradation variation on mechanical characteristic of rockfill materials with better-quality parent rock.