Salinity intrusion is an important issue which affects greatly economic activities and livelihoods in coastal downstream in general and the lower Vu Gia - Thu Bon river basin in particular. With the aim of making a plan to exploit water efficiently on the basis of applying natural law, the study used the Delta model to simulate the salty flow into the Vu Gia - Thu Bon river system. Using the input data (river bed data, water supply system, flow, water level, river water salinity, etc) that were processed synchronously for the period of 2016- 2017, the Delta model gave results consistent with the measurement data with a fast processing speed, low error level, high Nash coefficient, etc, which is very suitable to the conditions of Vu Gia - Thu Bon river system. These result are the scientific basis for the management of water exploitation projects in downstream areas in the short and long terms to respond to the increasing salt water intrusion into the river.