Abstract: Traditional homogenization models are difficult to accurately describe the mesoscopic effects of aggregate distribution, aggregate particle size, and steel bar configuration on stress wave propagation paths and energy dissipation mechanisms in concrete, which limits the in-depth understanding of the anti-explosion failure mechanism of reinforced concrete slabs. To address this issue, a three-dimensional mesoscopic finite element model of reinforced concrete slabs including steel bars, aggregates, and matrix was established based on the combination of MATLAB and LS-DYNA. Among them, aggregates were modeled using real aggregate gradation characteristics, steel bars were accurately arranged according to actual engineering layout parameters, and a reasonable contact algorithm was adopted between the matrix, aggregates, and steel bars to simulate interface effects. The model was verified by comparison through contact explosion tests, and the results show that this model can relatively accurately predict the failure mode and crater size of reinforced concrete slabs under contact explosion loads. On this basis, the effects of aggregate (distribution mode, particle size) and steel bar arrangement on the anti-explosion performance and stress wave propagation of reinforced concrete were studied through mesoscopic numerical simulation parameter analysis. For aggregate parameters, the particle size distribution characteristics and particle size of aggregates determine the evolution law of stress waves and energy dissipation characteristics, thereby affecting the geometric dimensions of craters on the TOP surface and spalling craters on the bottom surface of concrete. When the aggregate particle size is distributed in a decreasing manner from the TOP surface to the bottom surface, it can effectively inhibit the expansion of craters on the TOP surface and the development of spalling on the bottom surface; an increasing distribution will aggravate surface cratering and internal spalling damage. In terms of particle size, the spalling craters on the bottom surface of slabs with small particle size aggregates show shallow and wide characteristics, while those with large particle size aggregates show deep and small morphology. Compared with aggregates, steel bars have a weaker impact on the overall failure mode and stress wave propagation of the slab; under low reinforcement ratio, steel bars hardly affect the dynamic transmission process of compressive stress peaks, while under high explosion loads, steel bars inhibit the fragmentation process of the slab, alleviate bending damage, and improve the structural integrity and anti-damage capacity of the slab.