Abstract: This study investigates the effect mechanisms of rubber particles (RP), macro-synthetic fibers (MF), and their combined use on the mechanical properties of concrete, through uniaxial compression tests on macro-synthetic fiber reinforced rubber concrete (MFR-RuC) with varying RP replacement ratios and MF dosages. The particle size of RP ranged from 0.25 to 6 mm, and after pre-mixing it satisfied the grading requirements of Zone II fine aggregate. Meanwhile, computed tomography (CT) was employed to characterize the mesostructure of MFR-RuC, and the influence of these mesostructural features on the compressive strength of MFR-RuC was quantitatively assessed using grey relational analysis. The results show that the energy absorption and dissipation effect of RP and the bridging effect of MF contribute to enhancing the ductility of concrete. When used in combination, the failure process becomes gradual, cracks develop fully, and the inclination angle of the main crack increases. The compressive strength of MFR-RuC decreases with increasing RP replacement ratio, whereas the incorporation of MF provides a slight improvement. The optimal improvement of MF was observed at an RP replacement level of 30%, where the compressive strength of R30F0.5 was 13.43% higher than that of R30F0. Their combined use enhances their mutual dispersion, the incorporation of RP positively influences the angular distribution of MF, and MF contributes to the segmentation of large pores and guides paste flow, thereby slightly reducing pore size. The grey relational degrees between compressive strength and the mesostructural parameters are ranked in descending order as specimen homogeneity, pore structure, and MF orientation distribution. The mechanism underlying the evolution of the mechanical properties of concrete under the synergistic action of RP and MF was explored at the mesoscopic level, establishing a link between the macro-and meso-scale behaviors of multiphase composites and providing methodological support for the design and optimization of high-ductility concrete.