The invention provides an energy efficiency state diagnosis method of wind turbines based on an energy flow. The diagnosis method includes the steps that a relevant parameter library of a energy efficiency index of the wind turbines is constructed; a index parameter reference interval based on probability distribution statistics is confirmed; a wind power energy efficiency diagnosis tree is established; a level of energy efficiency state based on multivariate fuzzy recognition model is determined; a diagnostic result of energy efficiency state is obtained; and a real time diagnosis of the windturbine energy efficiency status is realized. The problem of incomplete and inaccurate state evaluation information of traditional wind turbines is solved. The accuracy of real-time identification ofthe wind turbine energy efficiency operation state is improved through an operation condition identification method.