Abstract: The macroscopic mechanical properties of materials are closely related to their microscopic parameters. The quantitative correlation between them is explored based on the theory of particle flow code. The microscopic parameters are confirmed through laboratory tests on marble under loading and unloading, which are suitable for brittle materials (such as marble), so as to provide the foundation for microscopic analysis of the unloading failure mechanism of brittle materials. The results show that: (1) Young's modulus of parallel-bond is the main controlling factor of macroscopic Young's modulus, and there is a linear relationship between them. Poisson's ratio is the polynomial function of Young's modulus of bond. The main objects of debugging materials of Young's modulus and Poisson's ratio are Young's modulis of parallel-bond and contact. (2) The joint action between the mean parallel-bond normal strength and shear strength influences the stress-strain curve of materials, and the mean parallel-bond normal strength is the polynomial function of the peak stress. The relationship between the mean parallel-bond shear strength and the peak stress is a log function one. (3) The essential reason for diversity of crack distribution is the relative relationship between normal strength and shear strength of particles: the failure type is conjugate damage when the ratio of the mean value of parallel-bond normal (shear) strength to the standard deviation is around 1; increase or decrease of the ratio causes the change from conjugate to shear damage, and increase of the mean value or standard deviation of parallel-bond shear strength causes the change of the direction of main failure surface. (4) The secondary failure surface of samples decreases with the increase of friction coefficient, however, the direction of failure surface will not change. (5) The macroscopic mechanical properties of marble tests show that the basic reasonable microscopic parameters can be obtained through orthogonal tests.