In order to study the influence of initial microcrack parameter distribution on fracture characteristics and mechanical properties of brittle rocks and further understand systematically the fracture evolution of brittle rocks， a two-dimensional mesoscopic elastic damage model of heterogeneity was established based on the theory of elastic fracture mechanics.The proposed model scheme was implemented through the two dimentional finite difference program FLAC^2D.The zones in the model behave elastically before failure occurs, and lose tensile or shear load bearing capacity at corresponding mode of failure.Microcracks with different length and orientation distributions were defined in the zones of the model.The failure of the zone was controlled by the fracture propagation status of the microcrack inside.A failure criterion was adopted based on the stress intensity factor of the microcrack in each zone.The fracture process of rock specimens with different morphologies under distinct loading conditions was simulated using the proposed numerical model.The influence of the microcrack distributions on both the macroscopic fracture pattern and the mechanical response of the numerical model was analyzed.The results show that when the microcrack lengths and orientations are defined by different distributions，the different macroscopic fracture modes can be resulted.When the microcrack lengths and orientations are defined by normal distribution， failure band with clear shape can be formed.Failure zones are relatively dispersed if the microcrack lengths or orientations obey uniform or exponential distributions. For the reasons of shear failure and splitting failure of rock samples during the uniaxial compression test of brittle rock， the initial microcrack orientation was of guiding significance.When the mean initial microcrack orientation ɑ=45°， the minimum peak strength and axial maximum strain of model were obtained.The fracturing process of brittle rock uniaxial compression test， Brazilian splitting test and fracture toughness test were simulated.Good consistency was obtained with respect to both the mechanical response and fracture patterns.The model is valuable in rendering reliable results for rock mechanical tests which are difficult to realize in the laboratory. The inclusion of the influence of microcracks in simulating mechanical behavior of rock material also provide important insights into the failure process of rock under external load.