Abstract: In order to investigate the influences of structural heterogeneity on the mechanical properties and crack growth of rocks, the microstructure of granite is modelled by using grain-based model (GBM). In comparison with the results of laboratory experiments, the properties of stress-strain curves, acoustic emission and grain-scale crack growth of rocks with different mineralogies are investigated. The results show that GBM can be used to efficiently study the macro- and micro-mechanical properties of rocks when the mineral components have different structures and strengths. The grain-scale cracks in rocks are mainly intergranular cracks at the onset of loading, then the intragranular cracks become predominant inversely, and the failure pattern of cracks is always dominated by tensile cracks. When the model fails, the ratios of intergranular and intragranular cracks to total cracks are about 93.87% and 60.95%, respectively. During the whole loading, the locations of microcracks are first located randomly, then the clustering of microcracks leads to the appearance of macroscopic failure surface, and the formation of failure surface is related to the propagation and coalescence of intragranular cracks. When the feldspar mineral in rocks increases, the corresponding peak stress and damage stress increase due to the increase of intragranular cracks formed in feldspar mineral and the decrease of intragranular cracks formed in biotite mineral. In this study, the modelling of micro-structure based on GBM and the reason why heterogeneous rocks behave different mechanical properties may promote our understanding of the influences of rock heterogeneity on the mechanical properties.