<p>Rock–concrete composite structures are widely utilized in transportation systems, energy infrastructure, and defense facilities. Research on the mechanical properties of composite structures can provide theoretical foundations for disaster prevention and control in major engineering projects. Static compression tests were carried out on rock–concrete composite (RCC) specimens after high-temperature treatment. The failure modes, stress–strain curves, and thermal damage of RCC specimens were analyzed. A three-dimensional mesoscale model of RCC was developed, which incorporated zero-thickness cohesive elements to simulate the mechanical behavior and failure characteristics of the rock–concrete interface. The results indicate that as temperature increases, the plastic damage characteristics of the concrete layer intensify. The rock layer exhibits axial splitting failure, with a main crack dominating the failure process. Multiple cracks develop in the rock layer at temperatures exceeding 400&#xa0;°C. As the rock proportion increases, the failure mode of the concrete layer transforms from oblique shear failure to splitting failure. The rock layer adjacent to the interface is more prone to splitting failure, forming longer damage cracks. The mechanical properties of RCC specimens degrade with rising temperature, and the plastic characteristics of the stress—strain curve become more pronounced. The established finite element model and the material parameter calibration procedure can accurately simulate the compressive behavior of RCC specimens after high-temperature treatment. The absorption energy of the composite specimens decreases with increasing temperature. The absorption energy of the composite specimens decreases with increasing temperature. Increasing the rock proportion significantly enhances the absorption energy of the composite. This enhancement effect markedly diminishes at 500&#xa0;°C.</p>