So far, coastal erosion in low-lying coast has always been a typical problem. Recently, along with development of economy, infrastructure has been widely constructed, which results in propagating shoreline retreat in coastal area. Cua Dai beach is a typical case. It has been eroded rapidly in recent years and the coastal erosion has severely impacted the local tourism industry. This study aims to analyze the geomorphic change in Cua Dai beach and Cua Dai river-mouth by using the numerical simulation and evaluate the effectiveness of anti-erosion countermeasures. The change of sediment transport near the river mouth were considered by comparing the sediment transport rate in the past (1990) with that at present (2016), using three-dimensional beach transformation model. From some results, it is assumed that the asymmetric distribution of sediment input from the river can occur in present estuary and it is supposed to be main cause of the severe erosion of left coast area. Based on such characteristic of morphology change, the countermeasures (e.g.: beach nourishment) to correct the imbalance of longshore sediment supply from the river and slow down the coastal erosion were considered in this study.