In view of the increasing ecological environmental problems in Shiyan City, water source area of the Middle Route of South-to-North Water Diversion Project, a composite ecological system for Shiyan City is established. By using the energy value analysis method to draw the diagram of system energy value, the composite ecosystem energy value index system for Shiyan City is established, and the change rules of the composite ecosystem energy value index in Shiyan City from 2003 to 2016 are calculated and studied. The results show that: (1)The energy output of the complex ecosystem in Shiyan City increases, but its self-sufficiency decreases, and its dependence on external resources increases. (2)The output of energy value contributes more to the economy, but the external exchange of interests decreases after the project is in operation, the living standard of residents and the utilization efficiency of energy value per unit area increase, the pressure of environmental governance increases, and the waste discharge is effectively controlled. (3)The complex ecosystem gradually turns into high consumption type, and its sustainable development capability decreases. (4)Compared with those of other cities in the water source area, the composite ecosystem of Shiyan City has strong energy self-sufficiency, environmental-bearing capacity and sustainable development capability; however, its economic development and residents' living standard are relatively low.