本文针对粘性不可压缩水流建立了拉格朗日观点下的能量泛函，通过变分法论证了能量泛函的一阶变分为零等价于水流运动的基本方程式，即动量方程式。在恒定流的条件下，利用拉格朗日函数导出了推广的伯努利方程，从而说明了寻找的能量泛函的正确性。 In this paper, the energy function under Lagrange’s point of view is established for viscous incompressible water flow. The variational method is used to demonstrate that the first order variation of energy functional is zero, which is equivalent to the basic equation of water flow, namely the momentum equation. Under the condition of constant flow, the generalized Bernoulli equation is deduced by Lagrange function, which shows the correctness of the energy functional of finding.