To ensure the ecological service function of the rivers in the main urban area of Taizhou City, this study constructed an ecological water demand calculation method suitable for this area based on the analysis of the characteristics of the rivers in this area. This method comprehensively considers the requirements of flow velocity, water level and water quality, and uses MIKE11 hydrodynamic water quality model to quantitatively determine a river water allocation method which can achieve ecological flow velocity, ecological water level and water quality goals. The calculation results have shown that the ecological flow velocity of the main urban river network is 0.1 m/s, and the ecological water level threshold range is 1.8~2.24 m. By fully utilizing reclaimed water as a clean water source supplemented by river replenishment, Taizhou’s main urban river network is meeting the target requirements of water level, flow velocity and water quality in wet years, normal years and dry years. This study provides a decision basis for rationally allocating water resources to maintain ecological health of rivers and lakes in urban river network areas.