Abstract: Accurate identification of mesoscopic parameters are the precondition to conduct the discrete element simulation reasonably. Based on the optimization theory, an automatic method for identifying mesoscopic parameters of sand material is proposed in this paper. The PFC software is used to simulate the biaxial compression test of a kind of standard sandy soil. By minimizing the error between the stress-strain curves obtained by conducting the PFC biaxial compression test and the laboratory test, mesoscopic parameters are identified automatically by using the mode search method. Numerical results show that the stress-strain curves obtained by the numerical simulation and the laboratory test agree very well with those based on the mesoscopic parameters obtained by using the proposed method in this paper, with high efficiency and accuracy.