Abstract: In order to meet the market demand and optimize the insulation process of hydro generator stator coil,the single VPI process of hydro generator stator coil is studied from the aspects of impregnation resin selection,process trial production and test analysis. The process comparison test is used to make sample bars respectively,verify the process,and formulate and optimize the process flow of single VPI of stator coil. Finally,through the normal dielectric loss tangent and its increment test and breakdown test,it is concluded that the normal dielectric loss,increment and breakdown field strength of coil insulation with improved VPI process can meet the standard requirements.