This study investigates the microcracking nature in mode-I fracture of hard coal, a material with strong bursting liability, using acoustic emission (AE) and particle flow code (PFC3D). The microcracks are represented by AE moment tensors (MT), which correspond to displacement discontinuities involving opening/closing and sliding motions. The source parameters of microcracks, including shear/tensile type, volume, orientation, motion, and magnitude, are calculated by minimizing the errors between analytical and measured displacements. The detailed fracture processes, including microcracking source mechanisms and energy dissipation during coal tensile failure, are analyzed using both experimental and numerical approaches. The results indicate that the microcracks exhibit a mixed-mode mechanism with both normal and tangential displacements, and their orientations are generally parallel to the direction of crack propagation, aligning with the expected fracture mechanism of mode-I opening. The AE inversion results for dissipated energy and crack opening displacement are consistent with those calculated from energy release rate G and DIC measurements. A new AE MT simulation method based on particle motion is developed using PFC3D to verify the reliability of the microcracking characterization. The mechanical properties and AE responses from PFC3D simulations are in good agreement with experimental results, reinforcing the accuracy of the microcracking characterization. The study provides a new approach for characterizing microcracks in loaded rock/coal, enhancing the understanding of meso-processes and mechanisms during rock/coal fracture.This study investigates the microcracking nature in mode-I fracture of hard coal, a material with strong bursting liability, using acoustic emission (AE) and particle flow code (PFC3D). The microcracks are represented by AE moment tensors (MT), which correspond to displacement discontinuities involving opening/closing and sliding motions. The source parameters of microcracks, including shear/tensile type, volume, orientation, motion, and magnitude, are calculated by minimizing the errors between analytical and measured displacements. The detailed fracture processes, including microcracking source mechanisms and energy dissipation during coal tensile failure, are analyzed using both experimental and numerical approaches. The results indicate that the microcracks exhibit a mixed-mode mechanism with both normal and tangential displacements, and their orientations are generally parallel to the direction of crack propagation, aligning with the expected fracture mechanism of mode-I opening. The AE inversion results for dissipated energy and crack opening displacement are consistent with those calculated from energy release rate G and DIC measurements. A new AE MT simulation method based on particle motion is developed using PFC3D to verify the reliability of the microcracking characterization. The mechanical properties and AE responses from PFC3D simulations are in good agreement with experimental results, reinforcing the accuracy of the microcracking characterization. The study provides a new approach for characterizing microcracks in loaded rock/coal, enhancing the understanding of meso-processes and mechanisms during rock/coal fracture.