Coastal sand shrimp farming is a new technology to raise farm on the coastal area in Vietnam since 1999. This new technology has turned a large intact coastal sand area into shrimp ponds by digging ponds covered with plastic sheets and cement consolidated edges. The rapid development of coastal sand shrimp ponds have brought in such main environmental impacts as ground water depletion, loss of forest and agricultural land partly due to salinity invasion; increasing sand storm; loss of onshore sea products and decreased shrimp yields due to pollution. This study provides a spreadsheet model for local authority to make decision on land use using cost benefit analysis as a decision tool. This study shows that despite of yield risks, individuals still have incentives to continue with existing unsustainable farming practices as this activity is financially profitable on average. However, the net social benefits of this practice is negative.