Abstract: Desiccation cracks can be formed in clay soil during drying, which connects with each other to generate a network. This process involves multi-field coupling effect, including water, thermal and stress. A close-packed model is used to simulate the formation of desiccation cracks. The simulation is based on the 3D discrete element modeling software MatDEM that is independently developed by Nanjing University. In the model, a discrete unit represents an assembly of soil particles, pore and pore water. Elements in the model are assigned moisture properties, where the transport of moisture can be simulated based on the Finite Difference Method. Furthermore, the coupling of moisture field and stress field is built, which considers the influence of moisture on the tensile strength of soil. In numerical simulation, assuming the water of soil surface evaporates at a certain rate, element diameters and mechanical parameters are calculated from moisture according the experimental data, so as to simulate evaporation, shrinkage and cracking processes of clay soil. Numerical simulation results coincide with the laboratory results, and each step of cracking process can be well simulated. This paper provides an alternative way for the numerical simulation of soil deformation and failure under multi-field effect.