Material scientists face a critical challenge in characterizing the mesoscopic damage evolution of concrete under tensile loading, as traditional experimental and theoretical approaches struggle to resolve the complexities of its multiphase heterogeneous structure. This study addresses this gap by employing the Discrete Element Method (DEM) with PFC2D to model concrete’s mesoscopic cracking, integrating aggregates, mortar, interfacial transition zones (ITZ), and pores. Through parameter calibration against experimental data, uniaxial tensile simulations reveal how aggregate percentages (30–45%) and pore percentages (1–6%) influence crack propagation and tensile strength. Specifically, when the aggregate percentage increased from 30% to 40%, the peak tensile strength decreased by 26%, while increasing from 40% to 45% led to a recovery in strength. With porosity increasing from 2% to 4%, the peak strength dropped by approximately 3%, and further to 6% caused a 14% reduction, demonstrating the quantitative impact of microstructural parameters on concrete performance. Simulation results align closely with experimental data, validating DEM’s efficacy in modeling mesoscopic cracking. This work provides a mesoscopic theoretical foundation for optimizing concrete’s tensile properties and underscores the need to incorporate realistic mesoscopic features in future simulations.