Abstract: Reviewing the upsizing development of electric machines,we can notice that the development of cooling technologies is crucial for the upsizing process.In other word,the upsizing development history of electric machines is also the development history of cooling technologies.Firstly,this paper briefly introduced the characteristics of three kinds of cooling methods for hydrogenerators.Secondly,the paper focused on the selection bases of cooling methods and put forward the new selection idea based on the comprehensive effect of reliability,maintenance and economic performances.Then,it showed the industrial applications of the evaporative cooling technology.The last part of this paper pointed out the development trend and application prospect of the evaporative cooling technology on the basis of the technical features and the real industrial application status,which give a useful reference to the cooling solution of the electrical equipment.