Abstract: The discontinuous deformation analysis (DDA) is widely used in numerical simulation of rock mass due to its capability to deal with large deformation and large displacement of a block. However, this method is rarely studied in simulating seepage field, especially transient seepage. Based on the steady-state seepage model established according to the cubic law, the unsaturated two-dimensional Richards equation is discretized and the transient global seepage matrix conforming to the DDA scheme is derived. The DDA transient unsaturated seepage fluid-solid coupling model for the DDA is established by acting the water head matrix as the external load form on the block. The correctness of the model is verified through the numerical simulation of soil column infiltration, sand tank infiltration tests and dangerous rock mass engineering cases, which provides a new method for the DDA to deal with the transient unsaturated fluid-solid coupling problem.