Seawater intrusion into coastal aquifers is a serious problem, leading to shortage of water supply in Tra Vinh province which is a typical coastal province in Mekong Delta Vietnam. One of the main reason for salinity intrusion is excessive abstraction from groundwater. In addition, climate change is an uncertain challenge which may affect the situation in the future. GMS groundwater modelling is an effective tool to simulate groundwater flow and salinity transport processes in this research. A conceptual and numerical model were built and calibrated to simulate groundwater flow in the case study area located in Tra Vinh with the use of hydraulic head data accumulated in the period 2006 to 2017, a sensitive analysis has been conducted on hydraulic conductivities, specific storage and conductance of boundary condition in order to understand model behaviour. Model results show that groundwater is overexploited in Tra Vinh province. Groundwater levels were continuously decreased in the whole area and in all aquifers. Groundwater recharge is limited due to impermeable layers on surface and is recharge is only possible in sand dune areas. Groundwater abstraction supplies domestic water demand which is much more than recharge. The sensitivity analysis shows that hydraulic conductivity is the most sensitive factor impacting the vales of the groundwater heads. Hydraulic conductance of the boundary is the most sensitive parameter under the head-dependent flow boundary, and hydraulic conductivity is the least sensitive parameter. However, specific storage is more sensitive to impact the values of change of storage. Thus, Boundary conductance, hydraulic conductivity and specific storage coefficient are important parameters for the accuracy of the model results. Saline groundwater occurs in the coastal zone and in the north area. Saltwater intrusion occurs in these area. The salinity data availability is too limited to provide a clear description of salinity distribution in the area.