This paper presents a numerical modelling study on the simulation of the cracking process and fracture energy in concrete under high strain rate. To capture the stress wave effect and the damage evolution at the meso-length scale, both a homogeneous model with a millimetreresolution mesh and an explicit heterogeneous mesoscale model with random polygon aggregates are employed. The tendency of development of a) discrete multiple cracks, and b) spread tensile damage across adjacent element layers, in the high strain rate tension regime is scrutinised. This phenomenon generally gives rise to an increase in the dynamic fracture energy, which is consistent with experimental observations. Relative comparison between the homogeneous and heterogeneous mesoscale simulations suggests a sensible effect of the mesoscopic heterogeneity in the dynamic fracture process.