Harmonizing different water use objectives in water system planning and management in the context of changing natural conditions and development requirements under pressures of market drivers emerges as an urgent issue in Vietnam. Through review and assessment of available applications of modeling simulation and optimization approaches in water resources and reservoirs system, the article proposes an application of combined non-linear programming and Pareto optimization to solve the ptoblems of water resources planning and management GAMS technology is assessed as a suitable tool for the analysis and optimization of the complex systems of river basins and reservoirs in Vietnam. In order to develop researches and practical applications of the system optimization methodologies and tools, it is essential to establish good environment for information exchange between researchers and system managers and operators as well as with stakeholders for the sake of well understanding advantages of system optimization in ensuring the transmission of information on transparency and clarity of the optimization methodologies, the flexibility and simplicity of the optimization tools and the quantification of optimization application effectiveness to decision makers.