The paper presents a dynamic model for a NDBEPR (Nitrification Denitrification Biological Excess Phosphorus Removal system) that achieves combined biological removal of nitrogen and phosphorus. The model includes the biological reactors and the secondary settler. A computer simulation programme was developed in order to test the model that was verified with reference to an existing urban wastewater treatment plant with a three-stage configuration (anaerobic, anoxic, aerobic reactors). The comparison between the simulation results and the actual plant recorded outputs shows that this model is able to well reproduce the dynamic behaviour of the plant.