<p>Extreme floods have severe adverse effects on the environment. Typically, the degree of impact is measured using scores or specialized ecological indices, which can be difficult for the public to understand. Since floods harm the environment by reducing ecosystem service values (ESV), we developed a method to quantify ESV loss from extreme floods as a measure of environmental damage. First, we identified four key factors influencing flood-induced environmental damage: flood depth, duration, plant height, and waterlogging tolerance of plants. After analyzing their ecosystem impacts, we developed a method to quantify the ESV loss rate due to floods. On this basis, we established a computational framework for quantifying ESV reduction at both unit scale and regional scale. A case study was conducted to validate the feasibility of the method. The results showed that: (1) The method can quantify flood-induced environmental damage in monetary terms at both micro and macro scales. (2) The environmental damage shows spatial variability, influenced by the four primary factors and ESV distribution. For the first time, we proposed a methodology to calculate the ESV loss rate caused by floods and employed monetary indicators to quantify the extent of flood-induced environmental damage. This method not only helps people easier understand the environmental damage, but also provides support for the quantitative assessment of comprehensive flood losses.</p>