[Objective] This study aims to investigate the evolution of uniaxial compressive mechanical behavior in rock-filled concrete (RFC) with different rockfill morphologies, elucidate the effects of curing age (3 d, 7 d, 14 d, and 28 d) and rockfill morphology (block and pebble) on the mechanical properties of RFC and self-compacting concrete (SCC), and establish the conversion coefficient between the cubic and prismatic compressive strengths of RFC. [Methods] Compressive strength tests were conducted on cubic and prismatic specimens of SCC, block RFC, and pebble RFC. Failure modes and stress-strain curves were monitored to assess peak stress, peak strain, elastic modulus (defined as the slope of the ascending and descending segments of the stress-strain curve), and strain energy density. The compressive mechanical behavior was compared between SCC and RFC, between block RFC and pebble RFC, and among specimens with different sizes. [Results] From 3 to 28 days, the cubic compressive strength of RFC was consistently higher than that of SCC at the corresponding ages. However, at 28 days, the prismatic compressive strength of RFC was lower than that of SCC, and RFC showed more vertical cracks than SCC. This difference resulted from the weakened constraint effect of SCC on the rockfill skeleton during prismatic compression. The conversion coefficient between cubic and prismatic compressive strengths of RFC was determined to be 0.461. Compared with block RFC, pebble RFC exhibited higher cubic compressive strength, while block RFC demonstrated higher prismatic compressive strength. However, pebble RFC exhibited markedly lower peak strain, fewer vertical cracks, and lower energy dissipation than block RFC. This difference was attributed to variations in the void space of the rockfill skeleton caused by morphological differences between blocks and pebbles. [Conclusion] The rockfill skeleton in RFC contributes to the increase in cubic compressive strength from the early curing stage, and this strengthening effect increases with age due to improved interface bonding resulting from continuous hydration. The weakened hoop effect in prismatic specimens reduces the matrix constraint on the rockfill skeleton, leading to lower prismatic compressive strength and a unique conversion coefficient for RFC. Rockfill morphology significantly affects the mechanical behavior of RFC. Block rockfill improves ductility and energy dissipation through mechanical interlocking, while pebble rockfill increases cubic compressive strength through dense filling. The established strength conversion coefficient and the identified rockfill skeleton-matrix synergy mechanism provide essential theoretical and data support for the mix design, performance optimization, and engineering application of RFC. Future research should focus on multi-age tests of pebble RFC and the effects of rockfill morphology on other mechanical properties to facilitate broader engineering applications of RFC.