Water flow under vegetated environments is a noteworthy research topic in environmental hydraulics and restoration ecology, and this research is particularly important for maintaining water transport and streambed stability in water ecosystems. The calculation of the resistancecoefficient in vegetated water flow is the core of this research. But there are still problems such as complex expressions and low simulation accuracyin this research field. To solve this scientific problem, this research, based on the theoretical study of environmental hydraulics and genetic algorithm, selected three basic parameters of vegetation submergence, resistance length and curvaturedegree, and successfully constructed the formula for calculating the resistance coefficient for flexible vegetated flow by usinga wide range of data sets. New quantitative relationship between the drag coefficient and the relative roughness of flexible vegetation was establishedin this study. The formula ofdrag coefficients for flexible vegetation conditions has a more concise form and can besuccessfully applied to both flexible andrigid vegetation.Asflexible vegetation is deformed under the action of water flow, and the quantitative expressions of Vogel number and relative roughness are given quantitatively through the analysis of its physical properties. Overall, this study improves the basic theoretical study of vegetated flow in environmental fluid dynamics and provides scientific theoretical support for vegetationrestoration.