Sand drain is the representative construction technology for ground treatment by drainage consolidation to deal with the soft foundation. The usual settlement calculation for the soft foundation and the prediction method are defective. Using PFC2D, we set up a two-dimensional model and simulate the process of settlement on heaped load for sand-drained ground with two dimension discrete element. Using 2~7 cluster units of different combination modes, we embody the porosity of the soft foundation, improve the model and analyze the changing rule of water level in the settlement process. The computed results basically tally with the measured ones.