Abstract: In order to explore the boundary effect of the desiccation cracking process, multiple sets of drying tests are carried out using the containers with different bottom roughnesses. Two different forming patterns can be observed in the laboratory tests, initiating from the top/bottom, and there is propagation closely related to the sample/container interface contact conditions. This verifies the boundary effect of the crack propagation. In order to understand the internal mechanism of the desiccation boundary effect of the soils more deeply, a discrete element model is established based on the drying tests. A water loss rate gradient parameter along the depth is introduced innovatively to simulate the change of the evaporation condition of the upper boundary of the soil samples. By setting the friction coefficient of the bottom surface, the contact condition of the lower boundary of the sample is simulated. The simulated results are compared with the experimental ones and found to have good agreement. In general, the initiation and propagation of desiccation cracks are the result of the combination of water loss due to surface evaporation and bottom friction. When the coefficient of friction of the bottom surface is relatively small, the development of the fracture is dominated by water loss, and most of the fractures develop from the top surface. With the increase of the friction coefficient of the bottom surface, the effect of the contact condition of the bottom surface on the development of the crack gradually increase, and the proportion of the number of cracks developed from the bottom surface increases accordingly.