Abstract: This paper analyzed the characteristics of environmental flow in plain river network areas. By using dynamic weight，a calculation method under different water quality and quantity combinations was designed. The environmental flow data of Songpu Bridge on Huangpu River were used to assess the environmental flow situation in Shanghai area. This research might provide a new way to understand, describe and calculate environmental flow guided by multifunction of river management.

Key words: environmental flow, dynamic weight, calculation and assessment, river network plain, environmental flow, dynamic weight, calculation and assessment