The purpose of this study is to investigate the bonding performance of a cement-based composite composed of 3D printed concrete (3DCP) and mortar. The 3DCP technology is suitable for fabricating 3DCP-based formworks, which can function as molds during construction without the need for removal and subsequently serve as structural components. Therefore, securing adequate bonding performance between 3DCP and the infill material is essential to ensure the structural safety and long-term serviceability of 3DCP-based formwork systems. To achieve this objective, experimental and numerical approaches were adopted. Composite specimens consisting of 3DCP and mortar were prepared using two infill mortar mixtures: a mixture identical to 3DCP and normal mortar. Splitting tensile tests were performed to evaluate the interfacial bonding performance. Small-sized composite specimens were designed for micro-CT analysis to characterize microstructural features. From the micro-CT images, pore and solid characteristics, including porosity, pore size, and the density of hydrated phases, were investigated. Regions of interest corresponding to 3DCP, mortar and the interfacial transition zone were defined. A pore morphology database for each region was also established. For numerical analysis, virtual specimens containing reconstructed pore structures from micro-CT data were generated. The reconstructed specimens exhibited microstructural characteristics almost identical to those of the actual specimens. Using them, Virtual splitting tests were conducted using a crack phase-field fracture model. The simulation results were compared with the experimental findings. The results indicate that pore distribution characteristics strongly influence bonding performance of the composite. Furthermore, differences in solid density between 3DCP and mortar promoted crack propagation along the interface. The proposed approach can be utilized to compare bonding performance using reconstructed specimens that mimic actual characteristics according to printing conditions, such as nozzle shape and layer height. This research can also be used to evaluate the degradation of bonding performance due to material deterioration.