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