Due to the means of the unsustainable exploitation and usage of water resources and environment in almost all river basin in Viet Nam, it leads to deplete the water resources, pollute the environment and degrade the river ecosystem seriously. One of the efficient solutions of the environmental management is that using the economic tools. This paper has presented an overview of the economic evaluation methods for the goods and functions of the ecosystem and applied them to compute these values for downstream Tra Khuc river basin by means of setting up the mathemetical functions to manifest the economic values of the goods and services of the river ecosystem downstream. The field survey data has been used for evaluating for two scenarios: present - 2010 and in the past - 1979 that corresponding to two different water resources conditions. The total economic value of the river ecosystem downstream Tra khuc river consisting 10 services and functions has been estimated at about 224 billion dong, approximately 0.03 percent of Quang Ngai GDP in 2010. Based on this, the integration of the economic values of the river ecosystem into the problem of water allocation in order to ensure the equality of the water stakeholders downstream including the minimum flow for the environment.